Front suspension is really nice to have, but a full suspension has some downsides.
They are heavier, and some of the power you put into pedaling is lost / absorbed by the shock instead of propelling you forward, this can suck for climbing / going up hill. Higher end suspension designs and rear shocks deal with this better, some have lockouts for climbing too.
Nice entry level bikes are the Specialized Hardrock, Specialized Rockhopper, Cannondale F5/F7. There are some cheaper options also that don't have the big name to go with them but are quality. Really component makeup is more important than who makes the frame. This Alpine is a pretty solid setup, Deroe components, Avid Disc Brakes, nice fork, nice wheels, etc.
http://www.ibexbikes.com/Bikes/ALP-650-Details.html
I'll see if I can find some more in the $300-400 range (new) when I've got some time.