Re: which entry level DSLR?
All these cameras are so darn good that it makes little difference which you choose.
I would suggest that Canon and Nikon have a much larger selection of additional lenses if you are thinking about upgrading later.
Re: which entry level DSLR?
I'm gunna try to steer you away from the nikon. It's a nice camera, but for the money, the other two are better. Just the AF motor is worth it, in my opinion, not to mention the extra 4 mpx. Also Sony has more lenses than most people think, because the minolta (sony) A mount has been around thirty years.
Have you considered these?
olympus e510 two lens kit
olympus e420 two lens kit
I didn't price shop - I just went to amazon because I knew they'd have good descriptions. I know you can find them cheaper. You'll get the same "other systems have more lenses" lecture about olympus, but they do have a lens for every focal length, so it is a moot point. The e4xx series are the world's smallest DSLRs, and the kit lenses smoke the kit lenses of any other company. The E5xx series has image stabilization like the sony - which is a really nice feature.
Re: which entry level DSLR?
GET THE A700. It is LEAGUES beyond the other 2, the D40 is nikons barely entry line, the Rebel is Canon's OLD entry level, the A700 is sonys top dog (not entry level by any means) - it competes with the Nikon D300 and the Canon 5D. It is absolutely no competition between the 3 you mentioned...
I am however skeptical, maybe you meant to say A200 or A300.... In which case I would still go with either of those sony's. A more fair comparison would be the Sony A100 to the Rebel XTi, at which point the Nikon is still beaten out. The a700 is certainly not "entry level", and $750 is half of what its actually going for.