As concepts go, here's one we wouldn't be surprised to see sprout into a commercial release in the very near future. Weng Jie's solar camera strap is designed to not only let photographers eke out a few more shots, but to do so making use of the sun's energy rather than bulky external power packs.
Rather sensibly, the strap basically replaces the neck cord most DSLR users wear to keep their cameras readily to hand with a solar-cell encrusted version. Clipping on to the camera's mounting points as normal, it would also have a DC plug to gradually top-up the DSLR's battery during use. Of course you'd need sufficient sun to make it worthwhile, so indoor photographers probably shouldn't bother, but anyone out and about should be able to hammer through a few more frames at least.
Jie also envisages some integrated batteries at each end of the strap, so you could feasibly charge up before you left the house (from a regular AC supply) and then simply augment it with solar power. Either way, we imagine that if the price was right this would be ridiculously popular with photographers, and we're expecting to see production versions spring up imminently.