What iOS apps will take pictures and not send them to Photo Stream by default?
Since Photo Stream backs your Camera Roll, any app that uses its own storage space rather than the Roll should do - and I doubt many have been (or can be) updated to backup their own storage to Photo Stream at this early stage.
I'm a fan of Camera+, myself. It saves photos to its own storage, and lets you push them to the Camera Roll (and, therefore, Photo Stream) if and when you want to.