If you've got money to kick around, check out the latest from Apple....
20-inch screen iMac G5--it's $1900....the 17inch is a fuckin bargain at $1500, but they're both ridiculously sweet desktop computers.
The 17inch powerbook kicks ass if you want a laptop....I stage managed a play that apple sponsored, and they donated one so we could mix live audio at each performance, holy crap was that fun.
If you're a PC user, I'd go for a new Dell, those function pretty well, and they're not too expensive. I'm a mac user myself and think they just make more sense, plus they're better for my side job as an audio engineer. My favorite thing about macs is that all the programs aren't linked, so if one program freezes, you can force quit that program without having to shut down the whole damn computer-windows is screwy and annoying that way.