if you're looking at a Canon 450D also consider a Sony A350
And don't forget the offerings from Nikon, Pentax/Samsung and Olympus. They're all good cameras, the feature sets are comparable if not the same; what actually matters more is the way they feel in your hand - get that right and you'll find it much easier to take pictures than you would with a "better" camera that doesn't suit you as well.
The only area where Canon has a clear advantage is third-party software support, especially in "free" (as in beer but not speech) applications like Deep Sky Stacker. But DSS is compatible with all cameras that can write 16-bit TIFF files, either directly or through the manufacturer's raw converter software. Raw support is convenient rather than a "must".
