Canon EOS Rebel XS and its successor, XSi, are pretty much the same camera, yet XSi has more to offer than its "younger brother" and is a bit more expensive. To choose between the two, you should first evaluate your budget and how serious you are about DSLR photography. If you feel you will take it on consistently and are willing to learn and improve yourself in the long run, then XSi is for you. Otherwise, my advice is to go for the entry-level XS and ever upgrade to something fancier if you will ever feel like it.
Here are the similarities and differences between the two models
– Both come with a DIGIC 3 image processor, with the only difference that XSi is 12.2 megapixels, while XS is only 10.1.
– The lens are compatible from one model to the other.
– Both work with SDHC and SD flash memory cards.
– The battery packs on both models are identical.
– Both cameras accept most Canon EOS accessories (I know there are one or two that do not work, but I do not recall them now, I have never used them)
– XSi can continue shoot 3.5 fps in RAW, whereas XS can only do 1.5 fps. In JPEG mode, XS is a bit faster, it can do 3.5 fps, while XSi only does 3.0.
– The LCD on the XSi is half an inch larger than the one on the XS: 3.0 "vs. only 2.5".
– XSi comes with HTP (Highlight Tone Priority), while its predecessor does not.
– XSi offers wireless remote shutter release, whereas XS is not compatible with either RC-1 or RC-5 protocols, so you will not be able to trigger the camera from a distance.
– You can only buy the XS with the lens kit, while with XSi you can purchase the camera body separately
At the moment I'm writing this review I truly believe that Canon XSi is the best Canon entry-level DSLR and perfectly fit for amateur photographers who have just discovered this new passion. I would recommend the XS model for budget constrained buyers; however, if you feel there are features in XSi that you might want to use, it's highly advisable to save some extra money and get the latter model. But if you feel that XS will satisfy your needs, you can safely go for it, and you will save money too.