The BEST RAM you can get most likely will be off of a website like www.newegg.com
. Personally go with DDR400 PC3200. Anything higher it won't run, also unbuffered ram. Buffered ram won't work.
Kingston is a very good brand, along with corsaisr. Partiot and GEil both are respectablein their areas of cheaper affordable ram.+
Also a cas lag of 2.0 is ideal, any other questions?