Recommendations are usually the following. Get PC3500 so you have a little OC headroom and it will be even more stable when running at PC3200 speed.
Stick with Major brand like corsair/ocz/kingston/geil/mushkin etc. Also you can check on asus site for the compatibility list...
For a more precise brand/model you need to tell us your budget.
Asus P4P800DX, P4C 2.6ghz@3.25ghz, 2X512 OCZ PC4000 3-3-3-8, Leadtek FX5900 w/ FX5950U bios@500/1000, 2X30gig Raid0