the most basic pre-designed kit i have seen is the Gigabyte 3D galaxy, i think thats the name. most of the major manufacturers like thermaltake and vantec have kits if you look around. i hear the site to go to is dangerden
depends on your budget. if you have $250-400 to spend on a really nice custom kit, go www.dangerden.com. most noncustom kits tend to be crap, but check out asetek's waterchill line. im putting that in my comp soon. you can see their kits at www.frozencpu.com