- you can find a good camera body and lenses from both Canon and Nikon. they have equally good systems in the market.
- what is ur budget?
- do you have personal preference now?
- 40D is bigger than Xsi and have more features as well... try it in the store to feel the body difference.
- for the lenses selection, you can skip 18-55mm. unless you know what you gonna shoot, you can start with some lenses such as 17-85mm or 28-135mm from canon.
- you can also search some reviews at www.dereview.com