I have the Canon S200 (2.0 mp, 2x zoom), and it's worked great. It takes better pics than the Pentax Optio S and Casio Exilim. It's certainly durable (I've got a few dents in the front, and the lens cover no longer shuts, but the camera still works fine), it can handle a little weather (note: it's not advertised as being weather proof), and it's certainly small and fairly lightweight. If weight and size are your primary concerns, I'd definately suggest the Optio S or Casio Exilim though. They're smaller and lighter, but as mentioned, the picture quality isn't as good as the Canon.
Also, digital zoom is completely useless, don't use it as a consideration.