From what I've found (also a photoshop user trying to figure out what I want for photoshop) a lot of RAM is important, personally I'm looking for about 8GB or more if I can afford it.
You'll probably want a lot of storage if you have heavy files or a lot of them, again personally I'm going for 1TB or more.
other than that I'm still trying to figure out which processor, I've heard from a techy friend that AMD is better for photoshop that Intel whereas Intel is better at seemingly everything else (was reffered here). I've been running photoshop CS4 on a pentium premium 4 XD so anything new is pretty much an upgrade for me. If I can run it on a there an intel i3 or i5 (keep in mind there's different generations) should be fine.
Any computer that fits that should do, I'm finding there are some avail. for around $507-$700 without tax