Be careful though, prices have stabilized after pit-falling for 3 consecutive months. Some kits have started to pick up steam.
My personal favorite is the Crucial Ballistix DDR667, 80$/2GB. Based on Micron D9 GMH, it's the best you can get for under 100$. Runs at DDR900 5-5-5-15 and 2.1V without a problem, or at DDR700 @3-3-3-9 2.1V.
In Europe they were 80€/2GB 2 weaks ago when I've bought them, now they're 104€.
Hope it helps.