Hi Kirk,
God bless you and may you always give Him the praise and glory for your new life. Full immersion, participant conscious baptism has always been a basic tenent of the fellowship of believers that join with the baptist denomination. In the half dozen or so baptist fellowships that I have been fairly well acquainted with, anyone can join as a member of the fellowship who professes faith in Jesus as their savior. You will usually be asked at that time if you have been baptized. It's up to you to be honest about whatever baptism you have received or even none at all. If you tell them that you have been baptized they will take your word for it, at least the ones that I've been involved with.
However, I'm not really concerned with what the leaders of any particular fellowship will allow as necessary for membership with them. The real bottom line is your security. Now, I am a born again believer who worships with a baptist fellowship although I don't refer to myelf as a baptist. I am a christian.
To me, denominations are a way to kind of know what a fellowship believes and follows. However, even within various denominational identifiers you will find the leadership of the individual fellowships may have some variations. This is why I always try to steer away from encouraging a believer seeking for a place to worship along denominational lines and rather encourage that they find a strong bible believing fellowship. There are many and there are many that are not. Yes, some of these divisions can be cut squarely down the denominational lines, but not all. Then you have various breakdowns within a denomination. For example: There is a denomination now that one branch is agreeing to accept homosexuals as pastors and leaders and the other remains steadfast that pastors and leaders are held to a higher standard. So, even if one looks along denominational lines, it is good to investigate what the individual fellowship where they will be worshiping believes about God, His Son, His Spirit and His word.
Having said all that. I find the baptist denomination is fairly consistent with the teachings of the Scriptures. We believe that baptism, much like communion is a symbolic command that we are told to participate in. There is much discussion about the actual intent and value of baptism in a believers life. I for one find plenty of Scriptural intent that if there is anyway possible that a believer, after making a confirmation of his understanding and intentions regarding the Lord, be baptized.
The argument against this is usually the thief on the cross. I'm convinced that there are a couple of issues specific to that circumstance that we may not be considering when we use it as a 'reason' to tell others that they don't have to be baptized. First, we don't know that he wasn't baptized. John the baptist and many of the disciples had been baptizing many of the people in and around Jerusalem which is where the crucifixtion took place. Secondly, the thief died before the Christ was raised from the dead. I don't believe water baptism was practiced in all of Israel before the Lord established it through his command. Therefore, if anyone is saved before Jesus' death and resurrection, then they probably weren't baptized and the thief on the cross would fit that timeframe.
Most importantly, I feel, is that we see that Jesus even desired to be baptized and when questioned about it said that it needed to be done. We have ample evidence that it was a regular practice for new believers to be baptized in the book of the Acts of the Apostles and finally we read Jesus' final command to his disciples. Go into all the nations baptizing them and teaching them to obey all that I have commanded you.
So, is it the baptism that saves? I think that while it probably doesn't save, it is certainly the first command to follow that shows everyone else and the Lord whether the words out of our mouth are true. We say, "Lord, I want to follow you." He says, "Be baptized." Whether you will or not is your first outward sign that your mouth is speaking what your heart believes. There are a couple of other passages in the Scriptures that also seem to point to another reason for baptism. It wasn't until Jesus was baptized that we see the Holy Spirit descending on him like a dove. When Anninias comes to give Saul back his sight the first thing he tells him is to rise and be baptized for the forgiveness of his sins. And, as you have pointed out, Jesus did seem to make it a very important issue regarding one's salvation in the passage of Mark 16:16.
So, my encouragement is to join which ever fellowship you believe best exemplifies and teaches the truth. I'm not familiar with all non-denom fellowships, but I know that some do practice believers baptism. If the one you are considering absolutely doesn't practice it, then yes, I'd be wary.
God bless you in your decision. Above all pray and ask God to give you an answer.
In Christ, Ted