I like using using Crucial, plus they have a System Scanner (also a Memory Advisor Tool), so you can see what memory your system can have.
http://crucial.com/index.aspx
If you don't want to buy from the Crucial website, you can always just use the Tool to see what RAM you can use and they buy similar type from a different maker.
I'm using some of their Performance RAM (Ballistix Tracer) in my Desktop at the moment. Works great :)

starcraft: "I and every PS3 fanboy alive are waiting for Versus more than FFXIII.
Me since the games were revealed, the fanboys since E3." 


Skeeuk: "playstation 3 is the ultimate in gaming acceleration" 









