OK, so as far as bikes, my background is as follows...
When i was younger i used to ride BMX bikes. I never raced competitively but my friends and i used to go to the nearest BMX track on off days and hit the doubles and race each other for fun. We also had a few different trails that we built and maintained pretty regularly. One was in an old landfill(pretty gross, but i'm still alive so no problems) that was basically a huge dirt/clay pile in the middle that branched off into a few runs. It was mostly big doubles and tables. We also had maybe 2 or 3 seperate trails that we built in the woods that were mostly technical rhythm sections with a few tight berms and stuff like that. We would ride street maybe once a month, but when i was at a street spot or skatepark i was usually skating.
Then i kinda stopped that, and mostly stuck to skating for a few years(skating has always been number 1 for me). Then about 4 years back i started riding a track bike. Again, never raced competitively, just mostly raced through traffic and went on a few group rides. Now i mainly ride for fun and to get from place to place. My bike is a Keirin Track bike set up with ProTaper 2" risers w/bmx grips so it's almost like riding a big BMX bike. It's very light and responsive and it's easily the nicest bike i've ever owned.
However, after noticing that my knees are starting to get old and i can't really skate for as long as i used to and i'd like to add another fun activity to my repertoire.
I really want to get into mountain biking. it's seems like a great way to get out and enjoy nature and whatnot. You can take it slow sometimes or can go all out and hit big jumps. But, because the sport contains so many elements it's hard to buy a bike because it seems like every bike is purpose built for a specific type of riding. Downhill, crosscountry, dirtjumping, singletrack, cyclocross, urban, etc. I'm not even totally sure what all of those terms mean.
so, can anyone recommend me a few bikes to look at when i start looking in a few weeks? I'd like to be able to ride trails, hit jumps, maybe bomb some hills. I'd like to spend under $800 if it's at all possible. I think i'd prefer a singlespeed hardtail bike for simplicity's sake. Front suspension is an option, but i'm not sure...