If you don't want to go with canalphones, as suggested earlier in this thread, the Sony MDR-7506/V6 (NOT 600!) might be the best fit from your list.
Most Sony in that price range is junk, but the 7506/V6s are a pretty good phone for the $$$. They're closed (good for dorm), good bass, well-constructed, and pretty comfortable. In addition, they can also be driven pretty well from a computer.
They can also be found for $60-$70.
My V6s are finally going to have to be replaced after a decade of service (I bought right after college and they've been through hell and back).
I'll be buying the Senn 280s, personally, since I need closed for my listening enviroment.
The 280s are nice phones, but slightly more expensive, have less bass, aren't known for comfort, and have an ungodly long burn-in requirement.
If you do opt for an open Senn, stay away from the 515s.
They're not highly regarded, and better open Senns are available for only a little more $$$.