I am using 2 x 1Gb ADATA sticks which I bought from Hong Kong on ebay which cost me just £72 including delivery!
Supposed to be 667MHz, but so far I have it at 850MHz without any voltage increase and it runs like a dream.
Running a core2 duo e6400 with 425MHz FSB.
Corsair 2GB TwinX XMS2 PC-6400 C4 works fine for me. If you are unlucky enough to receive a board with F1 bios, just get some cheap DDR2 ram so it boots, then change bios dimm overvoltage to 0.3, then return cheap ram for refund . Although i find it hard to believe any places are selling F1 bios boards. I bought mine about a month ago and it had F3.