Like Brian said, a Blizzard 1230 is great for compatability and a generous speed increase, a Blizzard 1260 has a little less compatibility but lots more speed - normally, I think its chip access maybe slow.... But, I would personally stay away from an 040. They run hot and from what I've seen have the most compatibility problems.
GVP is also a very good make, but its worth knowing their ram was non-standard and therefore not readily available.
