Would also recommend the SSD drive. However, I would go no smaller than 80GB, and personally wouldn't go less than 120GB these days. If you are a gamer, you may also want to go even bigger like the 240GB Corsair Force 3...which is $199 from NewEgg with a $20 MIR. Newegg.com - Corsair Force Series 3 CSSD-F240GB3A-BK 2.5" 240GB SATA III Internal Solid State Drive (SSD)
I'm actually thinking of getting that SSD for my box and moving my 80GB intel to another machine. I'm down to about 25GB free on my 80GB with BF3 and now Diablo III installed.