Corsair kicks ass because their staff is made up of people that actually try and overclock until it breaks. Then they take that experience and BIN only the best stuff to pass on the customer. Most overclock friendly RAM tends to be really really loose on JEDEC memory standards, where as Corsair clocks their memory appropriately. Plus, they work with the motherboard vendors for their memory profiles.
I had a set of Corsair XMS3 memory come in with one bad stick of RAM. I filled out their RMA form, indicated I was an advanced user and had done extensive testing already, and they got me an RMA # right away. No bullshit, no talking to techs who know less than I do, just got me a working set quick and fast. I've stuck with them ever since.
corsair memory rocks because you can also use it to comb your Fro. Dual purpose at its best. If they made that bad-ass power supply sitting in my case, then who am I to complain when they give me the memory modules to match!?!?