A&F, AE, Hollister, Forever 21, Volcom, Adio, Fox, Roxy, Quiksilver, Billabong, O'Neill, all those surf type brands.
Sometimes Junk Food and other graphic-tee shirt brands are popular.
There's like a sect of people (including myself) who are into Urban Outfitters.
And for the girls who can afford it, True Religion jeans are HUGE. I love their jeans- they're so stylish, long-lasting and comfortable!