I hear the PI series from G-skill is pretty stellar. but from my own personal experience with G-skill.. not the PI series. but regular. I currently have a 2x2GB G-skill pc2-8000 1000 MHz RAM. and it CANNOT get it's spec'd speed or timings. I can't hit 1000 and cannot get 5-5-5-15 with this RAM. even going to 2.3v from the stock 2.1 they recommend. All G-skill is binned in a way that it does not overclock. if it does. it's sold for the higher speed. so you usually get NO overclock with G-skill and I know that. as I can't even get close.
Anyways I currently am about to sell my current 2x2GB G-skill pc2-8000's and last night I ordered the Dominators. they are known to be one of the BEST. and can hit 1100 or more usually. get these.. on sale, with a rebate. and with paypal you get 15% off