So, we all like to play with our interpretation of the characters and their sexual histories and preferences. Canon gives us very little to go on with most of them. So I thought I'd write up what I remember of conversations and incidents and what that would imply to my mind as to the range of possible orientations, by the
Kinsey scale. For now, I'm only messing with those who are or have been main cast, which means Lorne, Caldwell, Zelenka, Heightmeyer, Cadman, etc. aren't in here. Feel free to discuss them, though, as well as what I've got here. Note, there are spoilers here, especially for "Sunday".
Teyla Emmagan
0 (Exclusively heterosexual) to 4 (Predominantly homosexual, but more than incidentally heterosexual)
Teyla gets teased in "McKay and Mrs. Miller" about her interest in a Marine. In "Sunday" there is a conversation about how she should approach "him".
Rodney McKay
0 (Exclusively heterosexual) to 4 (Predominantly homosexual, but more than incidentally heterosexual)
Rodney has shown genuine interest in various women, most notably Samantha Carter, and there was some genuine heat between him and hallucination-Sam in "Grace Under Pressure". On the other hand, he often seems to sabotage his own attempts to get close to women, so it's questionable how many relationships he's actually had (though his "I know what to do eventually" in "The Brotherhood" implies he's not a virgin).
However, John's comment that Rodney and Radek should "just make out and get it over with" in "First Strike" doesn't inspire any denials from either of them, which some might see as an admission.
He admitted to Katie Brown in "Sunday" that after seeing how happy his sister was that he'd like to get married someday. However, given he's Canadian, where gay marriage is legal nation-wide, this doesn't really imply much about his sexual orientation.
John Sheppard
0 (Exclusively heterosexual) to 4 (Predominantly homosexual, but more than incidentally heterosexual)
In a conversation with Ronon in "Sunday", John mentions being married before (which given his position in the US Air Force and the rarity of gay marriage in the US was almost certainly heterosexual) and admits it didn't work out. He has shown genuine interest in women in the show, most strongly to Chaya in "Sanctuary" (though he seemed rather stunned at the offer of actual sex in "The Tower").
However, he seems very open to the possibility that some of his friends and teammates may be gay or bisexual (conversation with Ronon in "Sunday" and comment to Rodney and Radek in "First Strike"), which may indicate his own preferences are a little broader as well.
Elizabeth Weir
0 (Exclusively heterosexual) to 4 (Predominantly homosexual, but more than incidentally heterosexual)
Elizabeth left an established heterosexual relationship to go on the expedition. She's also had flirtations here and there, including a significant one in "Sunday".
Carson Beckett
2 (Predominantly heterosexual, but more than incidentally homosexual) to 4 (Predominantly homosexual, but more than incidentally heterosexual)
Yes, that's right. I'm labelling Carson as some flavour of bisexual and canonically so. He's the only main character to have an established dating relationship during the show, that with Lieutenant Laura Cadman, which is begun in "Duet" and referenced in "Epiphany", "Critical Mass", and "The Return I". Likewise, his reaction to Perna in "Poisoning the Well" is quite openly interested.
Given that, it might seem strange to find him labelled bisexual, until you consider the episode "Irresistible" (Yes, I know you don't want to, but bear with me). Elizabeth describes Carson's behaviour toward Lucius Lavin as "smitten." That's a sexually-loaded term if ever there was one. You don't use such a term in regards to a friendship or mere respect. This is a word for someone who is very much in love. And Elizabeth, a diplomat who chooses words carefully, uses it of Carson toward another man. Significantly, no one seems at all shocked at the thought that Carson might be smitten with another man, nor does Carson deny it. While Carson's choice to bring Lucius to Atlantis is seen as odd, the fact that he's smitten with another man is apparently no cause for concern.
One also has to wonder what about their first kiss being while Laura was in Rodney's body strained the relationship so that it eventually led to them going their separate ways, as he admits in "The Return I". Could it be that the female body she had wasn't the one that turned him on?
Ronon Dex
0 (Exclusively heterosexual) to 4 (Predominantly homosexual, but more than incidentally heterosexual)
"Sateda" established that Ronon had a female love of some sort who was "close enough" to a wife ("Sunday"). When John asks if he's dating anyone, Ronon asks "You mean like a woman?" which is probably a strong indication that he's primarily attracted to the opposite sex, though it's possible he's clarifying the term based on his observations of Earth culture seen with the Lantians. While John brings up the possibility of him dating a man, Ronon admits he isn't ready to date yet.
Aiden Ford
0 (Exclusively heterosexual) to 6 (Exclusively homosexual)
So far as I can recall, Ford's sexual history is a complete blank.
Other interpretations will work if you consider the possibility that a character might be actively hiding his/her sexual orientation, in denial about it, or still exploring or coming to terms with it.
So, what have I missed? How does your vision differ?