How you call someone of the LGBT community actually tells them a lot more about you than vice versa:
Homo - this means that you don't have any gay friends as they would tell you it is like a slap in the face or you are a conservative christian who doesn't care what hurt you inflict on others, or you are a regular poster to CF and have just picked up bad habits from those on Philosophy and Morality
Homosexual - you are uncomfortable with the idea of homosexuality and try to make it sound clinical and technical. Christians often talk about homosexuality which is offensive to lesbian christians because while homosexuality means same sex attraction (homo was used because it means same, not "man") they tend to only refer to men - so for instance in the response to the Anglican Winsor report a theologican says "Homosexuality contravenes the bible through the penetrative aspects of sex." - he sure isn't talking about lesbians.
gay - general term used throughout the english speaking world
Queer - this usually means you are either under 28 or a womyn's study or critical theory major.
Dyke - this means you either hate lesbians or you are one - it is one of those words of self description that have been taken back by the community.
Butch, Femme, Lipstick, earth goddess, Teddy Bear, Leatherman, Fairy, etc - I wouldn't recommend using these unless you are gay or lesbian and even then unless you know the people you are with as some are okay with the words and some arn't - specific description words - if you hang with gays and lesbians I would try to get a handle on what they mean or you will miss some of the humour
Wymyn, Womyn, Wimmin - if you are a guy, just back away! haha, no seriously, it means someone who is pretty serious about the history of male oppression and enforcement of male views through time so you kind of know what topics you might want to avoid (like never use the word Pornography if you want to escape in the next 30 minutes).
Homosexual lifestyle or Agenda - you are either someone trying to sell something at a pride event, a human rights worker or more likely a Christian who disapproves of gays. I can't think of the last time "Agenda" has been used with any of my friends in normal conversation - we don't have a lifestyle - we have a life.
Pride - a general term meaning the fight for equal acceptance and inclusion in all areas of society.
Partner - the general term for a committed gay relationship, also "life partner", lover, girlfriend/boyfriend, husband/wife. If you know someone gay and know that they have a significant other, Partner is the best word to use generally (i.e. "Is your partner coming later?").
LGBT, GLBT, LGBTTQI - these stand for lesbian, gay, bisexual, transsexual, transgender, Queer (if there is another Q it is for Questioning) and intersex. In the UK, it is LGBT because it was decided to put lesbians first due to their historical anonymity while in the US it is GLBT (probably because gays starting using the phrase). Ironically GLBT also shows the ranking of acceptance both in the world and within the community.
I recommend sticking with gay as it is near universally accepted for both genders, if you are welcoming people or something make sure to include Bi as bi people are not gay and noting that helps thier acceptance and inclusion - also Transgender is a good coverall for everything from Transsexuals, Drag Queens, bois, androgynous and straight transvestites - no one will be really happy becuase they are all different viewpoints and experiences but no one will be offended (maybe) either.
