I would like to know what is available currently in terms of
human-powered generating systems. I'm thinkng of a stationary bicycle
or some such configuration. In terms of ouptut, I guess either 120VAC,
or a DC output with enough current as to be able to charge up a car
battery in a reasonable amount of time. I've an engineering
background, so I don't need much in terms of theory of operation,
unless it is cutting edge stuff, or a discussion on which types of
devices, generators, alternators, etc, would be most efficient given
the limitations of human strength and dexterity. I'm more interested
in who is offering such products, how costly they are, and how big the
market is for them.

A noble experiment, but you might want to read this first:

http://computer.howstuffworks.com/question658.htm

You may be aware of the wind up radio ?invented? by Trevor Bayliss.
Aimed for the third world but largely bought as gimmicky presents.

http://www.ogormans.co.uk/windup.htm

Pain in the nether regions they are. Not exactly an original idea
either. So let your imagination run wild and ?invent? anything with a
handle and it?ll sell in droves to the affluent west.

BTW, I invented a refrigerator with a handle, utilising the
temperature change when rubber is stretched, running it through a heat
exchanger. Then when it is allowed to shrink, it gets cold. You are
very welcome to develop and market this device.

Best

The wind-up radio mentioned by guzzi is indeed a "pain in the nether
regions." I bought two of these devices, and a friend of mine bought a
wind-up lantern from the same manufacturer. All of these gizmos had
very short lives before their springs were sprung (SPROINNNNG). One of
my $59.95 radios lasted only four hours.

While the concept is an interesting one, it may be that a device of
this kind that is durable and reliable would be priced out of the
range of most consumers.

Check out this website
http://www.angelfire.com/biz/petflicker/page9.html

If you put human powered flight in google, you will get some
information. If I recal correctly a very fit human can produce two
horsepower for about a half hour with his leg muscles, before
exhaustion. That is 746 watts-hours = 62 amp hours = about what you
need to recharge one large car battery. Average persons howerer are
exhasted long before the battery is recharged and the efficiency is
low unless the generator is carefully matched to the person pumping
the peddles. Likely most exersize bikes can be equiped with a small
generator instead of the break/clutch arrangement which is typical.
Most any dc motor will run as a generator.   Neil

An alternator is also possible, but the peddling speed must be held
within narrow limits to get about 60 hertz and the load within rather
narrow limits to get 120 volts, unless you use a voltage regulator
which may be more than 1/2 the cost unless mass produced.   Neil