I’m looking specifically at building little robots, but I know that a lot of projects are made that much cooler if they’re not tethered to a wall outlet. Little lithium polymer batteries would be perfect for little projects, but I haven’t been able to find many suppliers. Sparkfun is the only one I’ve found that has the right idea:
I think they could be sourced cheaper considering there’s lithium ion batteries in most modern electronics like cell phones and mp3 players so they’re definitely mass-produced. In any case, I think it’d be an attractive offering.