You have more money to play with so look at faster hard disks (WD raptor or SSD) and more graphics power.
Look for a screen around 24", Samsung are doing some nice ones - a new range of LCD ones came out recently. Alternatively I think bit tech.net were recommending an HP one - see their most recent buyer's guide.
I will assume you don't have a monitor yet, and recommend the T260 ($400).
You are left with $660 for PSU and graphic card(s).
One possible solution:
Corsair 850TX ($140)
eVGA GTX 285 $320 (two of them)
That's $120 over budget, but I expect prices will drop a bit by mid-June.
If you want something even better, get a Corsair 1000HX ($200) and the two GTX 285 cards. That's $180 over budget, but again prices will drop a bit by the time you buy. The difference here is that with the 1000W PSU you can add a third GTX 285 card later. That's the fastest combination available these days - nothing beats the GTX 285 Tri-SLI. It's better even than two GTX 295 cards (Quad-SLI), from the benchmarks I've seen.
Lol, I would call on that gtx 285 + corsair 1000hx aswell, once prices continously drop, they should fit in there hopefully. If not, you can get the corsair 1000hx now and 1 gtx 285, then get the other gtx 285 later once you have the money.