There was a TV series on human powered vehicles, generators, water pumps, etc. I think on the Discovery channel a year or so ago. One of the projects was an alternator using the front wheel.
The guy epoxied several rare earth magnets to the rim (disc brakes?) and wound a coil for the pickup. Since the output of a moving magnet past a coil is directly proportional to the speed of the magnet it had a high efficiency, enough to power his lights and GPS receiver with just a few magnets. Magnets were scavenged from dead hard drives.
Since I'm kinda Scroogey, I only have basic cable. The channel would have to be Discovery, History, National Geographic or The Learning Channel. You could probably find the series searching their websites.
probably has a few how to's on home built alternators.