i dont think you could go wrong w/ Mushkin or Samsung. A lot of companies use Samsung chips, but I believe that Mushkin makes their own. I have never owned Mushkin, but I have Samsung now and it is great RAM. Another brand to consider is Corsair. They are considered by a lot to be the best RAM out there...but everyone has their favorites...so really...Corsair, Mushkin, Samsung, Kingston HyperX, they are all great. If you are looking to do dual channel, then look at the matched pairs - I dont know if Samsung makes matched pairs. But if you are just looking for one stick then shop around for the best price cuz they are all gonna rock. I think Kingston is having 20% off sale on HyperX PC3500. Check the hot deals forum for a link. And Geil is on sale at newegg...I have heard good things about that brand too.
-doug