The XSi uses a 12 Megapixel CMOS sensor and the D60 a 10 Megapixel CCD sensor. Is 12MP better than 10MP? It depends on your use, but having more Megapixels allow for slightly more flexibility with regard to cropping and still preserving image quality. A win for the XSi.
The XSi uses ‘Highlight Tone Priority’ and the D60 uses ‘Active D-Lighting’. What do they do? ? In a high contrast situation, for example, when shooting a backlit subject against the bright sky, the camera is not able to record such a large difference in contrast. So you (or the camera, if left in Auto mode) can either choose to preserve the highlights and let the shadows go black, or show detail in the shadows, and let the highlights wash out. In a manner of speaking, this feature compresses the difference between the shadows and he highlights, so more details in both can be seen in the output JPEG image. Another tie.
14-bit vs. 12-bit Data Processing:
The XSi churns out 14-bit RAW files while the D60 just 12-bits. This would make a (small) difference if you process your own RAW files, and probably no difference if you shoot JPEG. A (small) win to the XSi.
Both manufacturers offer very similar kit lenses with image stabilization/vibration reduction features. The difference is that Nikon is charging about 25% more for their kit lens, perhaps because of higher manufacturing standards? It’s hard to say without actually testing them out. But from the specifications, I’m going to give the win to the XSi.
If I was in the market now for a lightweight, entry level DSLR, and had no preference between Canon or Nikon, I’d place an order for the Canon XSi.