you can forget the 550uz...u might be awed by the fact that it has 18x zoom and all. and the fact it looks great. but it is difficult to use and it has some issues with image quality like Purple fringing and distortion when zoomed in.
it is also priced higher than the s3is which performs much better in terms of macro, image quality, sharpness and not to mention a better video mode

g7 produces some of the best images among the prosumers but it only has 6X zoom. it is also expensive. but if u dont mind the lack of zoom and like manual control then it is a good choice. it is as near as a dslr as u want