I was in a Reject Shop today when i saw that they had an iPhone Induction Charger for the 3G and 3GS models for only $10. This was in a catalogue a couple of months ago for $60, so they must be clearing them out.
How it works is that you put a supplied case on your phone and just lay the phone on the supplied pad, and shazam the phone charges. The pad can charge two iPhones at one time (but i guess you'd have to buy two kits to get the two cases - then you could charge 4 phones at once, but then you'd need 4 kits, but then you can charge 8 phones - i could go on forever!)
I have seen these in a few of the Reject Shops, and they have national pricing, so you should be able to get these at most shops who still have them.