I'll be eGaying it or selling it locally - thanks a lot for the info - it's a great help!
I just got off the phone with a friend who's co-worker recently sold their four year old Trek 800 for $250.
Here's what they recommend doing:
1) Get it totally cleaned up, everything, wheels, spokes, chain, everything so it's sparkling clean.
2) Get a tune up at your local bike shop if it needs one for adjustments, etc.
3) Make sure both tires are fully inflated, hehe.
4) It's probably best to sell your bike locally, check out bike shops, coffee houses, college campus bulletin boards, and your Friday, Saturday or Sunday newspaper ... whichever has the largest used classifieds section, list it in that edition.
5) When posting flyers consider putting up a very simple web site with picutures of your mountain bike, the maintenance, etc and your contact information.
If you put a little elbow grease into it you could easily sell it for $250, maybe more. Fortunately Trek makes great bikes and has a good customer loyalty, so finding a new owner shouldn't be that difficult.