Originally Posted by
Myosmith
Look for a used chrome-moly steel fixed (no suspension) mountain bike from the early 1990s. There are lots of them around. The Trek 800 series, Specialized Hardrock, Giant Yukon or Boulder, and many other major brands are out there and they can be had inexpensively.
That would be my suggestion as well. I primarily ride a road bike, but I have a 24 year old Trek that I use as a utility bike and for rougher stuff. Works wonderfully. Something like this would be very affordable for you and would likely suit your preferences:
Old Red by
Yo Spiff, on Flickr
Lurk in these forums and get an idea of what makes of bikes are good name brands, and what to look for. You can also post links to any Craigslist ads you might be interested in and get feedback on the bike.
Added: Read further and saw that you already bought a bike. Enjoy the ride!