I second uesgirl...I am a sucker for Old Navy yoga pants.
Be careful with American Apparel. If the pans have an elastic waistband or a thick one, the pants will look and feel awesome. I have a pair with a drawstring though and while they look hot, the waistband isn't really secure enough so the pants bag up at the top and don't stay on.
I'm going to fashion hell for this one, but I like Abercrombie sweatpants too.