This would do it --

http://www.hobby-lobby.com/video_camera.htm

And it'll take an external battery easily so you could use it, but it only does 640x480 pictures and that's pretty cruddy.

Really, the GoPro option would work well, and I'll bet it's pretty easy to add an external battery. Still, I wish more cameras had a "just take a picture every X seconds mode" -- it would be very nice for taking pictures from R/C airplanes, for example (which I do from time to time) -- just tape the camera to the plane, tell it to take pictures, and go fly.

(I actually bought a GoPro HD for exactly this purpose. (And taking video of bike rides and the like.) Though it arrived DOA and I had to send it back, so I'm still waiting for it to return so I can actually try it out.)

Edit: I bought my FlyCamOne2 a while back. Now it looks like FlyCamOne3 is out --

http://www.hobby-lobby.com/flycamone3.htm

which may take higher resolution still pictures. Or may not -- they don't give any details on it! (And we don't care about any wireless capabilities for this anyways.)