I am selling my blue Trek Singletrack 820 for $168. Bought for close to $270 when I came to Stanford last year and it has served me really well. It's got 21-speed Shimano shifters and derailleurs for quick and effortless gear shifts and I just got new rear tire tubes last week.

Also comes with a U-lock ($30 value) and a white multisport bike helmet ($35 value) that can also be used for skiing/snowboarding. See link below.

http://www.backcountry.com/giro-encore-2-helmet