Canon makes tremendous equipment as does Nikon - either would be a very good choice if those are the two brands you're considering.
I started Canon (35mm film) and now have their top of the line EOS-1Ds Mark II which is their best available. You're at the point where you need a camera that can do POS (the green zone) and also allow you to fully experiment with all the settings the Mark II can do (pictorially). To get a feel for the camera, go to a local store (Best Buy, etc.) and try out their Rebel Series. I bought one for my dad and he is now an avid beginner. He experiments all the time and has done a tremendous job learning the equipment. You can't go wrong with this camera. My sister has the same model and shoots only in the green zone - her photos turn out great!
The benefit is that you have an endless choice of lenses available and can add as many accessories as you can afford. Once you get comfortable with it, you can go with the fancier models that have more settings to tinker with. Unless you have the need for a high 'fps' capability, the Rebel is the way to go. There are a couple of models to choose from. The XTi is the one I got for my dad's birthday but if you want a similar camera with a full frame CMOS sensor, the 5D would be a great choice so you don't have to worry about image scale factors. Smaller CMOS sensors change the effective 'mm zoom' rating of the lenses. You might want to read up on this factor before you invest if you've got more money to spare for your first DSLR.
PM me if you want more details! I've had 4 Canon camers, 3 film and 1 DSLR and I've never had a problem with any of them. I'd be happy to answer any questions you might have on photography. I'm getting ready to set up a photography business to help pay for my equipment. I've got a wedding coming up in October that'll be my first. Car photos are really fun though - check out my site: http://nyobie.smugmug.com/Events
. I've got photos of a local Hot Rod show and also the Detroit International Auto Show, all taken with my DSLR. I love it!