there seem to be 2 popular setups as far as i've seen people discussing:
abit ic7 (and variants)
p4 2.6C
or
barton 2500+
abit nf7-s (and variants) *or* asus a7n8x (and variants)
you'll want (depending on your uses) at least 512mb ram. for regular uses, get name-brand memory (crucial, mushkin, etc). if you want to overclock, get performance name-brand (ie mushkin black lvl II, kingston hyper x, etc)
with the p4, get 2x256 kit to take advantage of dual-channel
for amd, dual channel offers marginal (<5%) increase, so you can get 1 stick here
for video cards, the high end choice seems to be radeon 9800 pro/xt (or at least those are getting the most discussions.. haven't heard much from nvidia 5900 but i don't think it'd be a bad choice either)
otherwise, a good mid-range (~$150) card would probably be either radeon 9600 pro, or some people like the ti4600/4200
hm well i think that's about it.. check around the boards for other threads, some of them have more component-specific discussions.
with ~$1k to spend, you shouldn't have trouble building yourself a very nice system!