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For those that prefer to just buy one that uses a bike:
http://www.econvergence.net/electro.htm

You can find all sorts of power inverters on eBay: http://electronics.listings.ebay.com/Parts-Accessories_Power-Inverters_W0QQfclZ3QQfromZR11QQsacatZ58020QQsocmdZListingItemList

An average laptop consumes about 50 watts.

I don't think so. That's a page off the OLPC wiki, it says that laptops average about 20 watts idle. This is closer to my experience.

On an IBM T-40, the power measuring tool that comes with the computer (software) shows the laptop will use between 16 and 18 watts on lowest power consumption and up to about 25 with everything maxed and some peripherals plugged in (wi-fi, usb-powered hard drive).

On a friend's macbook pro: I think the system normally runs around 20 watts, and will use 11-12 W minimum and 40 to 50 max. This is a modern model: the latest, highest end one released, not including these new ones that will be coming out in a few days.

Here's another link. They estimate laptops average 10 watts, and I suppose your laptop would draw less ehile you were pedaling their generator (the laptop being idle).

I just want to tell everyone that 50 W is a bad number to assume for laptops, and 20 W is much better, and google is your friend.

I built my own electric bike as a mobility aid to get to the local shops. I wear two separate leg braces and pedaling was not an option, I also have a very large steep hill between me and the shops. I bought the Slipstream Electric Bicycle plans and modified them a bit. I've had the bike now for over 4 years and I figure around 3,000 miles, very nice ride.

Max speed 29 mph in about 4 seconds (beat a few motorcycles from the stop, but only if they did not know we were racing)
Range 30 miles with new batteries.
Parts cost $2,000.
Since the photos, I've upgraded to downhill wheels and hubs w/disk brakes.

Wrong! Unless you have a DIY electric bike like the slipstream, http://www.econvergence.net/emb.htm, you just aren't going to go 30MPH.

Bikes in most of the USA are legally limited to 20 MPH. Those in many other countries are limited to about 15 MPH (25 kph). In any case most cut off the electric motor when you reach 20 MPH unless you tweak them http://www.chargerbike.com/tech/speed.html

There is currently one that sells for off road uses that doesn't will go 25 MPH http://tidalforce.com/products/m750x/specs.html $2749 is a bit steep, and it's still not legally allowed on streets and bike lanes. Knowing that the US is filled with scofflaws, I expect to see these soon.

I don't know if I've seen anything that stores energy from pedaling (b/c when you're riding you really don't want something dragging on the wheel & slowing you up). There were some kits that, I think recharged during breaking, but from what I remember because of the light weight of bikes (?), the amount of energy gained from this wasn't too great.

Do check out electric-bikes.com, it's an interesting website. I actually purchased plans to make a Slipstream Electric Bicycle, but it's a bit too much for me in both the money and being-able-to-put-it-together dpts.

Electric assist bikes or add-on's aren't uncommon.

Google for more if you're interested . . .

Build yourself a stationary bike with a generator on it, and use it to power your PC. What better motivation is there, than knowing that if you peddle too slow you'll lose all your data?

Except we didn't have to worry about freezing cold.

I did think my office should have invested in some kind of generating bikes to run the servers in case of a rolling blackout (where the elec company purposefully turns off the power to certain grids so the whole thing doesn't crash).

Exercise for us geeks and the company can still provide our clients access to their data. They didn't really think it was such a great idea.

We don't know who struck first, us or them. But we know that it was us that scorched the sky. At the time they were dependent on solar power and it was believed that they would be unable to survive without an energy source as abundant as the sun. Throughout machine history, we have been dependent on humans to survive. Fate, it seems, is not without a sense of irony. A machine's harddrive magnets attached to a human on an exercycle generates more electricity than a 120-volt battery and over 25,000 BTUs of wasted heat. Combined with a form of fluidised bed coal combustion, the humans have found all the energy they would ever need. There are fields, endless fields, where hard drives are no longer being used to store data. We just spin. For the longest time I wouldn't believe it, and then I saw the fields with my own eyes. Watch them gut the dead hard disks so they could be turned into alternators to power the living. And standing there, facing the pure horrifying precision, I came to realize the obviousness of the truth. What is the Matrix? Control. The Matrix is a computer generated dream world built to keep us under control in order to change a sentient machine into this.

I'm not sure the solar panel is worth the weight, or the danger of having something that expensive and fragile on the bike.

Suppose you had a bike like this one. The motor is rated at 1 horsepower but only uses more than half of that on hills and starting from a stop.

Half a horsepower is 373 watts. A half hour makes 187 watt-hours of power needed.
Let's say you were willing to wait an hour to charge the bike enough to run for half an hour.
Angling the panel dead-on to the sun on a good day will get you perhaps 60 watts of power into the batteries per square meter of panel.
But you don't want to carry around a square meter of panel -- the weight and wind resistance would eliminate any benefits. Let's say you could put up with lugging a third of that around, so we get 20 watts. It would take over 9 hours to charge the batteries enough for a half hour ride.

I would suggest a pedal powered generator would be a much faster way to charge the batteries. But if you were willing to pedal, you wouldn't have needed to attach all that weight to the bike in the first place.

There is a real audio interview with Ed Begley, Jr. over on EVworld and he brings up some things I found to be very interesting.

First, EV is a lot like the early VCRs, CD players etc. Everyone worried "are they going to stick around?" EV is in that stage right now. He pointed out that things like ebike.com are going to help turn consumers onto the idea of plugging in your vehicle when you get it home.

I am preparing to build an electric bike (note this is not going to be electric-assist). There is a cool one here.

Another place to check out is Esarati. They look pretty damn cool.