i'd say go to a place like FutureShop that has a bunch on display and try to figure out what you think you need and just get a general idea what is offered for the price range you are interested in. this is a good way to begin, then go to a website to get further into details about each camera.
i have an s100 as well and key things for me were rechargeable batteries, at least 2 megapixels, various capture sizes (640x480, 1028x864, 1600x1200), compact flash or smart card (as opposed to sony memory stick), optical zoom (strictly digital zoom is useless).
--craig