Well some things I could think of were, and I don't know what kind of comp you have now, but...you could:
Upgrade your RAM
Upgrade your Graphics Card
Upgrade your Sound Card
Upgrade your hard drive(s)
If you listen to music a lot: MP3 player
Games for 360, or PC
Thats about all I can think of right now...hope this helps!
X2, one of the best investments other than the stupid little issues you'll run into. and if the mod bug catches you, believe me its a bit more expensive than a computer