I've been watching a more expensive kit at Fry's for a while, but Ecotopia has a nice, more affordable (if you discount the shipping, I'm sure) Hydrogen fuel cell car.  Why am I ranting about the specifications for it?  Because I've already got my Micro .Net Framework board running off solar, but solar is much less desirable when you're demoing in a presentation room than when you're out and actually using the board.  A fuel cell (or a couple if it came to that) would be great for both staying off grid when we talk about remote sensor nets and the like, and would be useful as well to put in the bots to keep my impatient and OC self from playing the battery shell game with charged, discharged and partially charged battery sets between the wall charger and the bots themselves.