I think the Olsen's dropped out after like a semester because one of them became anorexic or something...and most of the Gossip Girl cast have probably finished college, but on the show like half the cast is going there so we'll get to see them filming around campus.
But you've probably heard of these guys:
Morgan Spurlock (he does documentaries like supersize me and 30 days)
Alexis Bledel (Gilmore Girls)
Felicity Huffman (desperate housewives)
Lisa Edelstein from House
Julie Benz (from buffy and angel)
M Night Shyama-something
Mara Wilson (Mattilda!)
Kristen Bell (gossip girl/veronica mars)
and that guy from Harry Potter/Twilight was filming here last week, but he's not a student...and this is just from what I've heard, I'm sure that list has more.