Originally Posted by
MRT2
You don't get much for $400 to $500. What you will find in mountain bikes at that price range are heavy, slow, and not the greatest quality. If that is your budget, go with a new hybrid like the ubiquitous Trek FX 7.x, Jamis Coda Sport, Kona Dew, Giant Escape, or Specialized Sirrus Sport. Any of those hybrids would make a much better commuter than any $500 new mountain bike.
Programen, this is where I would have pointed you. Some of the bikes mentioned (maybe all?) will take fatter tires, possibly up to 40mm, which might be attractive for those bumpy roads. Lots of good tires available in the 35-40mm range.
I would recommend taking your time, doing research and riding as many bikes as possible. If you want to haul a lot of stuff, make sure the bike has braze-ons for racks and then figure the cost of purchasing/installing said racks.