I'm running 2 150Gb raptor drives, used to be one for my OS and one for games I'm currently playing. Then I thought 'meh' and Raided them together (striped ftw). Now I run the games and os off the same drive(s).
Then I've got 3 1TB drives and 1 2TB drive (just got that today). The 3 1TB drives are for storage, the 2TB drive backs up my most important stuff.
edit: The other three drives are smaller, 2 500GB drives and one 250GB drive. The 500GB drives are also backup drives, the 250 has xp installed just in case.
I've also got 2 Summit SSD's, one 120Gb and one 250Gb. Then I've got 1 2.5" 500GB external, 1 2.5" 320Gb external, and 1 2.5" 250Gb external. I like space
total storage space: 7.990TB