If you look at the actual manufacturer on the RAM itself, most are the same two or three makers. For example, memory made by Hyundai is used in most new Compaq and IBM PC's that we are getting in right now. The same memory is sold at Circuit City, Micro Center, and CompUSA for low prices. I have also found that many of the labels on the packaging have this same actual brand of memory.
More importantly, match up the RAM types. If it is ECC you have, then buy only ECC. If you have a P3 with an 815 chipset, use only non-ECC RAM. And match up the speed and voltage for best performance.
H2H