Off the top of my head (When I was Christian, I did a lot of research on this
some open and accepting Christian Churches:
-Many Episcopal Churches
-United Church of Christ (UCC)
-Disciples of Christ (This church is very accepting of gay people, but also theologically quite conservative, and very "evangelical" (at least the one I visited) so gay/gay friendly Christians who fall into the "evangelical" camp would probably be at home here)
-Metropolitan Community Church (VERY open and accepting
-Presbyterian Church USA (Most of them anyway, but NOT Presbyterian Church in America (PCA) or Orthodox Presbyterian, neither of which is known to be very gay friendly, though I'm sure there are some acceptions)
-Religious Society of Friends/ Quakers (Like UU, not all Quakers are Christians, (like me, I'm a quaker, but not Christian), but it really depends on the group. Some Meetings are very Christ Centered, others not so much, others a mix. I attend a FGC (Friends General Conference) meeting. We have members who are very very Christ Centered, and others who are not. We are also very open and affirming
Independent Quakers I've heard are kind of like UU, but I don't know for sure, I've never been to a meeting. Conservative Friends are definitely pretty Christ Centered as a group, not sure about their stance on homosexuality though), and Evangelical Friends, are as I've heard, much like other evangelical protestants in many ways, and I would venture to guess, not super supportive of Same Sex couples, but again, I don't know for sure.
-UU of course (again, as was said before, the Christ Centered-ness really depends on the Church)
-Many Independent/Liberal Churches with protestant roots (though TYPICALLY not a church labeled "non denominational", they tend to lean VERY conservative, though again, I'm sure there are acceptations.
-Liberal Catholic Church - Don't know too much about them, but pretty sure they're gay friendly
Others to consider:
Evangelical Lutheran Church in America (ELCA), it really depends on the church, as a denomination they're getting there, I went to an ELCA church briefly, and never ever heard anything anti-gay. I've heard some ELCA churches are very open and affirming.
Christian Science, I don't think there is an "official stance" on homosexuality, I think it's something that's left up to the individual to decide
Reformed Church in America (RCA), Like many other "Mainline Protestant" denominations, I think they're "getting there" as well. They tend to be more liberal than the Christian Reformed Church (CRC). I like in a HUGE reformed area though so that might give me a bit of a different perspective. I don't believe that the RCA is exactly open and affirming, but in general they seem at least kind of accepting, I think there stance now is kind of a "we don't know, we can't judge" kind of thing, but again, I might be way off base here.
United Methodist, Some are really really accepting, others are really really not, it really depends on the church.
Some "Emergent/Emerging" Churches, but also some are not. Again, it's more of a "We don't know" kind of thing.
I'm sure there are others, but that's all I can think of right now.