Need advice

I just ordered some parts and need some advice on the memory. I can afford $200 to $250. I know I need 2 1gb dual channel sticks for 2Gb total, but the rest, and where to get it, is a mystery. I also would like to know what the least expensive SLI-capable power supply might be. Here’s what I bought today.
Abit Kn8 SLI
XFX Geforce 7900 GT Extreme
AMD 64 3800+ (venice)
ARCTIC COOLING Freezer 64 Pro

This is strickly a game computer, that’s why I went with the venice (single core)
Any suggestions?