If you want to spend less than $800. Maybe a Trek 4900, or Gary Fisher Marlin, or a Specialized Rock Hopper,(basic model) will do what you want. Use the left over funds to get shoes, cleats and fun accessory items. I myself want the GF Tassajara but that is a little more money. ($670)

Heck the Trek 820 is a good bike if you just want a blike to ride around. I would much rather have the 820 than that Y26 pogo stick. But that is just me and I am not a mountain biker either. I just like to ride bikes a lot and do things on the cheap.

Good luck.