I'm in love with Ada Wong since 2005

Most beautiful gals in gaming? Well, there's Rosa, Samus, Robin, Wii Fit Trainer, and Lucina. Those are quite the beauties... Oh wait, I listed off most of the gals in smash xD

That Frisk character in Undertale is pretty dang cute too. That is a girl, right..? x )

This cutie here:

I've also found Jill Valentine to be an extremely sexy woman, though I didn't like the make-up Capcom gave her for Resident Evil 5, battlesuit aside.

Probably Eleanor from Bioshock 2.

Aphrodite God of War III, Sam Until Dawn, Lara Croft Tomb Raider (next gen) 2013 (And you should be ashamed I am the first one to mention it).

Lara Croft

As a Brit I have to say Lara Croft.

However, I think a good shout has to go to Alyx Vance.

Fictional girls in videogames: I still prefer the first Lara Croft, even if by current standards she'd be considered a low-res polygon mess.
Real girls, either devs or involved in gaming in some other ways: Veronica Belmont.