There are good reviews on all these cameras on this site..
No one can make up your mind for you - you should not even ask for that..
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That question always generates responses from fanboys who claim that the camera they own is best because of blah, blah, blah. The best thing to do is to carefully read and compare the reviews of the cameras you think you might be interested in. Then come back to the forum with specific questions about the various models. We will be happy to help..
Incidentally, all three of the cameras on your list are excellent. The bottom line will be which one you prefer and will use the most..
Get somewhere where you can put your hands on the cameras. Both the mentioned cameras are small. They may be comfortable for you, for me they were not..
I wouldn't discount other manufacturers unless you have a reason for doing so. Pentax k100 probably gives the most bang for the buck and is a bit larger camera. Same goes for the Sony A100. Both have in body stabilization as a plus..
Olympus has a very small E410 and that can be purchased with twin kit lenses that are quite good. The E510 is a bit larger, adds stabilization, and can be purchased with the same two kit lenses..
Tha Canon kit lens is less than stellar, but the body is great. The D40/D40x has a less than full feature body, but the kit lens will perform better...
I choose canon Xti, mostly because I want to AF all the time, and I want my camera body to do this, rather than limited to particular lens (D40 and D40x require AF-S/AF-I lens if you need AF)..
Current Canon XT is about $440 (buydig.com) and XTi is about $600. With $100 rebate if you buy the printer together (MP970 or MP610), I think the price is hard to beat... $340 to 500, that's the price you pay for a P&S! And the printer itself qualify for another $40. MP970 will cost you about $220, and MP610 will be $150. Not too bad..
Nikon on the other hand does not have any rebate, as far as I can tell. As most of you here will tell you that there is not a clear winner, I think most of you here will also tell you that there is not a clear loser either. For me, it is AF in the body for me to pick Canon, and the more advance AF system in XTi that makes me pick over XT. I don't care too much about mega-pixel, dust removal etc for example...
Here's yet another opinion, this time from a fellow DSLR novice that recently switched from a Canon A620 (2 years) to G7 (2 months) to a Rebel XT. I didn't have as much loot to work with as you and did a huge amount of research to find what I thought was the best bang for the buck. I am super happy with my choices being a great starting point for entering into the DSLR world with limited funds. All I need now are decent wide angle and macro lenses..
I decided to go with the black Rebel XT body.
Canon EF 50mm f/1.8 II (The famous "Nifty Fifty" lens!).
And the Canon EF 28-105mm f/3.5-4.5 II USM Standard Zoom Lens.
If you were to get a Rebel XT or XTi and wanted better inexpensive lens to start out with the above might be something to consider though if you were to get the kit lens you would also have a decent wide angle. For a few weeks I had a Rebel XT with kit lens and I found that the wide angle was the only thing I was pretty happy with..
One thing to keep in mind about the Canon EF 28-105mm f/3.5-4.5 II USM lens is that around either end of the focal length and aperture settings the pix don't look good. Otherwise it can capture really sharp images with good color and contrastmuch better than the kit lens IMO. Others would probably recommend a somewhat more expensive and nicer lens for you to start out with but for my needs and situation this has worked out great..
The 50mm one is a no brainer if you decide to go the Canon route. Lots of people love that lens for good reason and it costs about the same as a good filter. With that one be prepaired to duck because the pictures will definitely be popping!.
Good luck on finding the right equipment for you and do handle the cameras in stores to see if they are a good fit for your hands...