the newest WD raptors will be the fastest for your needs, especially the 150GB ones. the newest 7200.10 (perpendicular recording) drives come fairly close, but for the most part, the raptor is still king.
however, i just wanted to warn you that the ONLY place you'd really notice a speed increase with faster hard drives is that games (and your OS) will load faster... you WILL NOT get more fps in your games and unless you do hard drive intensive tasks (video editing, multiuser environments), you won't notice any other difference. moreover, having two drives in RAID 0 doubles your chances of a drive failure causing all data to be lost but the performance increase is no where near double. you are also adding more noise/heat to your system using raptors.
so, IMO, the money would be MUCH better spent on a faster video card, more/faster RAM, or a faster CPU. if your system is already maxed out and you still have money to burn, go for it... but for gaming, i think it's a waste of money...