well, considering you havent specified your riding style, I think this might be a good option for your budget:
http://www2.trekbikes.com/bikes/bike.php?bikeid=1022610&f=18
These are "entry-level" mountain bike that are cost effective and very reliable. I have a friend that rides them in a very technical terrain. look for the list of dealers on the trek site.
Other companies that supply good entry level mtb: specialized, giant, merida, gt - there are many more.
