Kash recommended the G Skill RAM, so I ordered it from Newegg. I would highly recommend it. Shipping was quick and painless and the installation was relatively simple. I rarely ever shut my computer down, but for the two or three times I did shut it down, I noticed it started up much quicker with 2GB of RAM. Programs don't bog down so much anymore and my processor runs, on average, 2 to 3 degrees cooler than usual.
Of course, the gain was instantly noticeable going from 512mb to 2GB, and I'm sure gains would be noticed even with upgrading to 1,024mb.
Edit: At the price I paid ($90 with fast shipping), I'd say the 2GB purchase would be prudent.