[Lonewulf]

I take it you mean the comic books and not the movies. If you do, then I'd say pass in the movies as none really impress me as hot. Okay, I take that back.

Marvel:
Fantastic Four Sue Richards portrayed by Jessica Alba (note: in the first movie, not second movie. She looked retarded trying to be blue eyed blond. Second note: I thought she was hella stupid to portray Sue Richards. Regardless, Jessica Alba is hot.

In comic books, that's a little more tricky, because that depends on who drew them., who inked them, etc. But for simplicity, I'll stick to who drew them.
Marvel:
Excalibur:
Meggan by Alan Davis
Rachel Summers aka Phoenix by Alan Davis
Kitty Pryde aka Shadowcat by Alan Davis
(you could just rubber stamp any girl Davis drew. Here's a downside, Davis has a style where everyone looks related. Much like Scott Campbell, but while Campbell draws faces, torsos and thighs excellent, he sucks on calves feet and hands. the calves look monsterably long and feet look like a second calf)

Uncanny X-men Anna Marie aka Rogue by Jim Lee
(I'd say any girl Lee drew, but sadly, the man had favorites)

DC
Superboy and the Legion of Superheroes
Saturngirl aka Imra Ardeen by ...
Duo Damsel aka ... by ...
Phantom Girl aka ... by ...
Princess Projectra aka ... by ...
(Sadly, I wasn't interested in which artist drew which series at the time, because in my naivty, I thought all artists drew characters all the same. I THINK that the artist I liked who drew the female characters best was Joe Staton. But they all seemed to have favorites to draw too.)