First I will present everything that I think pre-wrath and post-trib generaly agree on. Then I will post the pre-wrath view. Then I will give my brief understanding of how the post-trib view differs and why.
The 70th week of Daniel represents a 7 year (360 day years) period. At the beginning of this period, the Anti-Christ will make a peace treaty with Israel. The world at large won't know that he is the Anti-Christ. Somewhere before this treaty, he will have gained the support of three nations. Over the 3 and a half years he will gain control of 7 more nations (people groups) for a total of 10. 3 and a half years into the 7 year treaty, he will break the treaty and reveal himself to the world as a tyrant who will persecute Jews and Christians in addition to anyone who doesn't accept the Mark of the beast as outlined in Revelation 13. After the 7 year (7 * 360 days) period, there will be two additional periods of time, a thirty day period and a fourty five day period (see Daniel, last chapter).
This is where we pre-wrath diverges from post-trib (post 7-year).
Pre-wrathers say that the AC's time of persecution will be cut-short before the second three and a half years are done. Now, since the AC is allowed to rule for the entire second half of the 7 years, the only way that the persecution of Christians can be cut-short without cutting short the ruling as well is by rapturing the church away from the persecution (or else protecting them on earth, but there is no suggestion about that in the Bible). In support of this position, the rapture is clearly tied to the day of the Lord (that is, it will occur at the onset of the day of the Lord; post-tribs believe this as well, but we disagree on when the day of the Lord begins).
Locating the onset of the day of the Lord itself is key to determining when (in realtion to other events since no mans knows the day or hour) the rapture will occur. Observe signs of the day of the Lord as given in the Old and New Testament.
Mathew 24:29 -- immediately after the great persecution, the sun will be darkened, the moon will not give her light, the stars will fall from the sky and the heavenly bodies will be shaken. The sign of the son of man appears in the sky and the elect are gathered from the four winds.
Luke 21:25 -- After the persecution, there will be signs in the sun, moon and stars. On the earth, nations will be in anguish and perplexity at the roaring and tossing of the sea. Men will faint from terror, apprehensive of what is coming on the world for the heavently bodies will be shaken. Jesus comes and our redemption is drawing near.
2 Thess 2:1-2 and 1 Thess 4:13 to 5:1-11 -- The rapture occurs on the day of the Lord which is after the anti-christs persecution. That is, it would occur just before the wrath of God (since we are not appointed to wrath).
Joel 2:31 -- The sun will be turned to darkness, and the moon to blood, before the coming of the great and dreadful day of the Lord.
Isaiah 34:4, 8 -- stars of heaven will be dissolved, the sky rolled up like a scroll, all the starry host will fall ... like shirveled figs from a fig tree ... for the lord has a day of vengeance
In summary: you have a darkened sun, a darkened moon (or bloody moon), stars falling from the sky, the sky rolling up like a scroll, shaking of the "heavenly" bodies, tossing of the sea (perhaps from a massive earthquake) and men fainting from terror at what is about to happen to them.
Now observe Revelation 6:12, the sixth seal. "There was a great earthquake. The sun turned black like sackcloth made of goat hair, the whole moon turned blood red, and the stars in the sky fell to earth, as late figs drop from a fig tree when shaken by a strong wind. The sky receded like a scroll, rolling up, and every mountain and island was removed from its place. Then ... [everyone on earth] ... hid in caves and among rocks... [they said] ... the great day of [God's] wrath has come and who can stand?"
That is the key to the whole thing. If that is the sign of the day of the Lord as it clearly seems to be, then the rapture should occur shortly afterward. The most immediate thing is the sealing of the 144,000 Jews in chapter 7. Just after that, in 7:9-17, a great multitude suddenly appears in heaven. They are described as those who come out of the great tribulation. The pre-wrath position posits that these are the newly raptured saints. If you carefully read the passage (especially the prayers and worshipping) it seems like a strong possibility.
In addition to all of that, if you look at Mathew 24, you'll see that Jesus gives some things that must happen before this sign of the day of the Lord. There will be false christs, wars, famine and earthquakes, great persecution of the church, then the sign in the son moon and stars will occur.
In Revelation 6, if you watch the seals, you have the mysterious White Rider (false christs or Anti-Christ?), Wars and Famine. Then you have death and hades given power over a fourth of the earth to kill by the sword, famine and death/plague and by the wild beasts of the earth. The Greek word for wild beast is the exact same word that gets translated "The Beast" everywhere else in Revelation. The pre-wrath position holds that this is an overview of the Anti-Christs persecution of Christians (the wrath of Satan). The fifth seal simply shows martyrs whose number has not yet been completed (this fits naturally with the AC's persecution having already begun). Then the sixth seal is the sign of the day of the Lord which suggests that the day of the Lord has come bringing the rapture in short order followed by the wrath of God against the earth.
Here is another key point of the pre-wrath view. To preserve the unknown day and hour, this rapture occurs at an unknown point during the second half of the 7 years. It would probably be closer to the end, but it cannot be exactly at the end for two reasons. As I just said, the day and hour must remain unknown, but in addition, there needs to be more than 5 months for the 7 trumpets to sound (since the fifth trumpet requires 5 months). Of course, this assumes that the trumpets are God's wrath, but this seems like a good possibility considering that they are after the sixth seal and that the nature of the trumpets suggests it (the trumpets are supernatural disasters as opposed to the natural disasters that occur in the seals prior to the sign of the day of the Lord; also, the locusts in trumpet 5 home in on anyone who doesn't have the seal of God on their forehead (the 144,000 Jews have it)).
Post-trib
The major difference in the post-trib view is that they insist that the "second coming" of Christ must occur at Armageddon because that is the only time in Revelation that Jesus clearly appears.
Against this view is the evidence I presented above that the day of the Lord began all the way back at the sixth seal. To fix this, the trumpets and bowls need to somehow occur concurrently with the seals (which is suggested against by the way the seventh seal opens into the trumpets). Or else, they have to deny that the sixth seal is the sign of the Day of the Lord.
I will never be able to deny that since the sign is so obvious. Naturally, the pre-wrath scenario requires that certain parts of Revelation be integrated into a single chronology (for example, chapter 13 must provide a "zoom in" view of the 4th and 5th seal. There is evidence that many chapters in Revelation provide exactly this kind of "zoom in" detail, so it is not inappropriate to do this. The only thing that is necessary to play with the chronology, is to watch for the breaks. Whenever John stops using words like "then" which imply a continuing sequence of events, they chronology may have been broken.
Another point against pretrib: Jesus seems to appear on the earth in Revelation 14:1 (mount zion is the mountain that Jeruselem is built on) which is before Armageddon anyway.
Defending pre-wrath
Now to address a few things that seem to go against the pre-wrath view. First is that the pre-wrath view requires a split "second" coming of Christ. In response to that, I first say: who said that there will be a "second" coming of Christ? The Jews did not think that there would be more than one coming of their Messiah. Why should we limit ourselves to one? In addition, whoever said that "Jesus" was going to leave after he raptures the church? He could leave bodily, but Jesus is God. If the day of the Lord has begun immediately after the rapture and the sealing of the 144,000, then why would anyone say that Jesus' second coming had ended and that the wicked are waiting for his third coming? Even if He isn't hanging around where anyone can see him, all kinds of crazy meteors and locusts are bringing his wrath on the world.
One more thing. The rapture is supposed to occur at "the last trumpet of God". In support of this, some people look to Revelation 11:15-18 which is the last of the 7 trumpets and which is after the pre-wrath rapture has occured. It says that "the kingdom of this world has become the kingdom of our Lord and of his Christ and he will reign for ever and ever." What this tells me is that the 7 years are over (leaving only the 30 + 45 days until the 1000 years start). Why? Well because the AC is given until the end of the 7 years to reign. Revelation 11:18 says "your wrath has come" according to my NIV. My NASB says "your wrath came". In any case, this surely doesn't override all of the evidence that the Day of the Lord began with the trumpets rather than beginning right here.
Finally, about "the last trumpet of God". In the OT, there is a story where God actually does blow a trumpet. He is calling Israel to battle a previous beast empire in the Old Testament (Revelation reveals that there will be 8 beast empires, the 6th was clearly the Roman empire since John said "the sixth exists now", the 7th was Hitler's empire, the 8th is the AC's empire -- the beast empires are primarily identified by their great persecution of Jews). Now, according to various OT day of the Lord prophecies, Israel will apparently be rallied by God at the onset of the Day of the Lord to begin fighting back against the Anti-Christ. I believe that the last trumpet of God is this rallying trumpet. It will occur at the onset of the day of the Lord and which is also when the rapture will occur. Thus, the 7 trumpets of Revelation 8,9 and 11 are not "trumpets of God" (even if God's angels are using them).
Those are the only major complaints that I know of against pre-wrath, and I think they are extremely weak compared to the propensity of evidence that the sixth seal marks the onset of the day of the Lord.
Questions JS?