i just bought the 07 redline monocog after returning an 07 GT peace 9r. great buy at $450 or so. i would recommend this as you would have $400 to upgrade whatever you like after you've ridden it. so far i've added On One Mary bars, ergon grips, and a brooks saddle and i'm still under $600. your other options include:

raleigh
khs
gt
motobecane
redline monocog flight

a surly karate monkey is $450 for frame and fork and it's seriously no better than the monocog, which is a complete bike at that price. read the reviews at mtbr.com, nobody is disappointed with the monocog.