Well, they’re also some of the only games that include actual romance, which I suspect has something to do with it.
Oh god, how could I forget about Annah ? I second that with my very soul. I loved her hyper-angry-but-really-shy-inside character. The tail is an obvious plus, but she could have been a hobbit for all I care. Neeshka from NWN2 cries herself to sleep because she’s not Annah.
Bah, Deekin was still awesome. He just doesn’t do anything for me.
In Half-Life 2 most people seemed to have a crush on Alyx Vance as has been mentioned several times already. For me it was Judith Mossman. It was clear that you were supposed to fall for Alyx. Guess what Valve, I happen to like that 35-40ish redhead scientist babe you put in the game more.
It was also pretty clear that Mossman had a thing for Eli Vance. Why do I always fall for the least attainable women?
The goth girl from FFX.
Can’t remember much about her, not even her name, but she was a very well, er, designed character.
Voiced by Seth Green, no less. That makes him twice as awesome.
I’m currently playing Vampire: The Masquerade: Bloodlines.
Jeanette. Hoo boy. I know they say “Never stick your dick in the crazy”, but sometimes you just got to, y’know?
And Velvet Velour can manipulate me alllll she wants.
Heather? Not so hot, actually. Makes up for it with her delightful personality, though.
Lulu. You can’t have her, she’s mine, MINE I TELL YOU ! 
Kerrigan, from Starcraft. Er - after she was infested. (I’m sick man, I need help.)
Oh trust me, I know. And that’s probably about 79.5% of the reason for my crush on him. hearts Seth Green fiercely
I can’t BELIEVE I forgot to include her on my list. Oooooooomg with the pixelly hotness. Crazy bitch indeed, but my digital self would do it all over again 
VV I wasn’t so crazy about. She kept talking me up and then when I finally finished her damn demands, not so much as a peck, much less a fade-to-black. :mad:
Something, but not everything. I mean, people have mentioned Tali and Garrus, both of whom are non-romanceable aliens. Tali’s face is mostly obscured by a helmet, and Garrus’ is covered with spiky bony plates.
Yay personalities! 
I see your point, but they’re in a game that has romance options, which I think just makes the omission of romance for them all the more glaring. Especially since the included romances are fairly bland. I mean… aliens abound in this game, and the romance options we get are two humans and one alien? Totally conducive to alien-crushing.
Celes (Final Fantasy 6)
Mew (Jet Set Radio)
Shenhua (Shenmue 2)