All the top names I can think of have been thrown out there already. Check out Cole Barash too, he's not quite a top gun yet but I really like his work.
Probably also want to check out snowboard photographers, as for a college research topic you're probably going to want to go a little broader anyway. Those would be Tim Zimmerman, Scott Serfas, Dean Blotto Gray, and Dano Pendygrasse to name a few.
I'm a photo major, so I have a HUGE list of photographers that I follow regularly, in pretty much all the action sports, and beyond. Send me a PM if you've got any questions/want to talk shop photo nerd style.