Good combination is an Asus A8N5X (or the A8N-32X if you want Crossfire or some other variant of asus if you want SLI) and an Athlon 64 3700+ or A 64 X2 4000+.
You're better off waiting right now though. Intel and AMD are lining up their new chip and board sets, and its going to be all out war (meaning dirt cheap prices for the consumer). When Intel launches its Conroe core design, you can either get the most powerful consumer CPU ever released, or you will be able to pick up an extremely competative A64 X2 4800+ proc for dirt cheap (that's what I'm waitng for anywhoo).
And you're looking for a board with PCI-E support, not PCI (totally different).
Hold off on the videocards too, since Microsoft Vista will launch with Direct X 10 support (current cards support up to 9.0c), so you can either buy a current gen card for cheap or a DX 10 card to be up to date.
Just hold off on the upgrade until around september this year and you'll be very happy. Hell, or upgrade now and be very happy, but don't complain.