I usually carry a small Casio EX-Z1050 which can give some decent photographs and is quick to fire up and take a snap or two. The battery life for this camera is very good, but I still carry a spare Lithium Ion cell just in case. With a 16Gbyte SD card it will take around 3000-4000 10 Megapixel photos or over 3hours of VGA video.

http://www.digicamreview.com/casio_exilim_ex_z1050_review.htm

Modern Camera technology is pretty amazing. Even 720p HD video is now being introduced into sub $200 pocket cameras.