You have to decide whether you want the increased portability of the super-compacts, the feature-richness of the somewhat larger P&S's, or the zoom of the significantly-larger "super-zooms." I have the most experience with the super-compacts, which I'll describe here.
I am the proud owner of both the Canon SD700IS (which is somewhat better than the newer 800IS, see reviews) and the Fuji F30. For low-light no-flash photography, as well as candids that require quick-release (think babies) the F30 is better than anything else on the market. It does like to ramp up to higher ISO's, however, so it requires some tweaking there to prevent an overly water-color image. However, for outdoor photography, I've always loved the Canons. The color is just vibrant and makes for great prints. One of the best features, which you really don't see on too many cameras other than the canons, is the ability to stitch together photos to make panoramas, which can then be turned into beautiful large prints or quicktime-VR files (really cool, if you've had a chance to play around). I've gotten some stunning panoramas from mountain-tops - you can get 180 degrees or more, which is not possible with even the best panoramic camera. For Niagara falls, I'd get the Canon SD700IS (or 800IS if the wide angle is worth more to you than barrel distortion).
Dave