Pic: Lar Hovsepian, 24, of Los Angeles charges her cell phone on a human powered bicycle generator with the help of Brad Whaley at the Coachella Valley Music and Arts Festival on Friday, April 27, 2007 in Indio, California.
Apparently, several of these were used at the Coachella Music & arts Festival for charging cell phones.
Parts list and instructions are available here. They even have a link to buy from amazon.com .
If you're not up for building it yourself, they also sell already assembled bicycle generators which range from $980 to $1,499.