From the maker blog a while back they ran a series of posts on joule theif.
Bill on the SolderSmoke blog ran a couple of articles on mechanically keyed transmitters, like the ET phone home rig, also a rew ideas around clock powered keying.
So my brain was buzzing away recently and it wasn't until I spotted the solar powered garden lights, that ceased to work a couple of months ago, that I thought about re-using them. The little solar cells only put out 0.8-1.1 volts. Three in series put out around 3.2 volts in full sun light. I need to go back and see what kind of current they can sink though...
To power something like an arduino keyed tx or a DC receiver with NE612, I would need a solid and regulated 5 volts.
It wasn't until this morning, on the irc channel of our local homebrewers, that I thought about mashing up the joule theif and the 80 meter DC receiver to make a solar powered radio =) It would make it limited to day light hours, but its certainly workable. Still have some other things to work on first, but certainly the next project on the list =)