After a lot of consideration, I bought an EX-S600 a few weeks ago and am very happy with it. Very small size and movie function were critical for me and I have a 2GB card. Excellent video (although see my post in the Casio section re video playback). The MPEG4 seems to be an excellent format and whilst you cannot use the optical zoom whilst filming, you can preset it and also use the digital zoom if essential.
PS. Good info on Casio and Canon in particular, inc Z750 & S600 reviews,and on digital photgraphy in general :