What should I look for in memory?

I'm looking into buying 1GB of ram soon, and I'm not sure exactly what I should look for when choosing the ram. The RAM will be used primarily for heavy gaming, like BF2, CoD2, and other games. With BF2, I've been getting 'low virtual memory' things, and all in all, I would like a 1GB stick of ram. I currently have 512mb. What kind of timings should I look for? Also, what's with the registered and unbuffered ram? Later on in the year, I'm sure I'll upgrade my mobo and processor. Any specific brands that are reliable for heavy gaming? The amount I can spend is about $175. I have an AMD Athlon XP 3200+.

Registered/Unbuffered memory are designed for servers, mainly because they use less power and don't stress your memory controller that much so they are able to run large amounts (more then 4GB's) at the same time.

If you are looking to upgrade to 1GB and you also plan to upgrade your mobo/CPU then OCZ's Platn Rev 2's is what you are looking for. Latest batches are TCCD chips and as I recall they are just as good as previous (clock up to 300MHz/DDR600 with fair timings and around 2.9V on Vdimm)

Here is a link for them: http://www.newegg.com/Product/Product.asp?Item=N82E16820146890