Cannondale F600
http://cannondale.com/bikes/05/cusa/model-5FS6.html
It's a great looking bike in my opinion, is a hardtail with disc brakes, but is toward the top of your price range.
For starters, go read the MTBR.com reviews on any bike you're considering. For example, the F600 is reviewed at
http://www.mtbr.com/reviews/2003_har...t_121463.shtml
BTW, Cannondale has a great frame warranty, and they have a trade up program if you wish to upgrade your frame at a latter date.