Max $120 at 20% ($600 deposit required). Details here:

If you want to try Pokerstars, this is the time. They don't offer signup bonuses (although I'm sure you can find some through affiliates), so this is you best chance for the next couple of months. They always offer one in conjunction with their WSOP qualifier tourneys, and those start this weekend.

By the way, Pokerstars bonuses never expire and you can withdraw the money before you clear it. Bank it now and come back after March Madness.