Get on DP Review, there is ton's of info about each manufacture and cameras.
www.dpreview.com
Its all about your budget and what you plan on doing with it.
Do you plan on getting into photography, or are you looking for something just to take some snap shots.
There are some really good Point and Shoot cameras like the Canon S5 IS. But if your looking for something a little more serious, and function. Then you can get a DSLR. The 2 most popular brands is Canon and Nikon.
If your looking at Nikon, id suggest going with something like the D50 or better. Because the D40 uses a different non common type of lens. The D50 is about 3 years old, there are alot of other models you can check out.
If you checked out canon id recommend something liek a 350D, 400D, or the new 450D (WHICH IS AMAZING!). These are great starter DSLRs, with Tons of room to upgrade.
The only Nikon id get would be the D3, but thats way to expensive. So ill stick to my Canon.
Ive only been into photography more seriously for about 3 months now. It becomes addicting if you really get into it.