On the outside, these groups may look like drinking clubs in which no one is actually friends at all. Try it from the inside, though, and there's a whole different story. At least this has been my personal experience. On the contrary, the reason Greek organizations sometime seem so homogenous is that they recruit people with whom they're going to have something in common. You don't have to be Grant Hill to succeed in college athletics.
Most universities have plenty of competitive athletic programs that operate on many levels.
IM, club, and varsity sports all fill their niches, and basically anyone can get involved. The arts are a great way to get involved on campus, whether that's photography and visual art, dance, theatre, music, or anything else in the category. It's also a chance to express yourself, which can be quite a relief when you feel overwhelmed by the huge number of people on a college campus.