that swiftech 655 is indeed a wonderful pump and i would recommend it to anyone who wants a easy to get, not that expensive and good performing pump.
but if you want the best:http://www.customaquatic.com/customaquatic/subsubcategorypage.asp?subcatindexid=wp-aq-sm
its the MD-20rlz (don't forget the z)
its probably the ultimate watercooling pump there is, huge amount of power, low noise, and a relatively low heat dump. there are more powerful pumps, but in a watercooling loop, they are useless as they have too much heat dump.