then you should simply just grab another stick of the same kingston you have man, it should be fairly cheap as well.....unless you simply wanted to get some better RAM and incase something happens to those you still have a 512mb stick on standy like I actually have.
TwinMOS makes 1gb of RAM for $100 that are also great OC'ers but requires a good amount of voltage to get them that way. Believe it's 2.5-3-3-7 stock timings.
Ooooh, it's now $85!
Of course that's in the US, but...man that's a deal and a half