Which DSLR should I get?

Well... that depends on what you want to do and what you already have. If you already have a Digital Single Lense Reflex (DSLR) , and a group of lenses for it, then you'll probably want the next generation from the same company. For example, I have a Canon Digital Rebel XT, a few nice lenses for it, batteries and the 430ex Canon Flash. If I bought a Nikon as an upgrade, none of my current lenses (or glass as we photo heads say) would work on the Nikons, so, I'd have to start all over getting new glass and accessories. Until Canon makes me really mad, or Nikon comes out with some over the top technology, I'm pretty much married to Canon.

If you don't already have a DSLR then it's wide open for you. This is a great time to be buying a DSLR ! The technology rocks and the prices are great! For some folks, the choice between brands can take on religous overtones, similar to the Mac vs PC world. For me, I'm in the "see which one you like the most today" camp. While there are minor technical differences between Canon and Nikon, they don't really make a whole lot of difference for most folks as long as you are comparing similar price points. The $600 dollar Canon is going to give you about the same quality image as the $600 Nikon. Ditto at the $1000 units and the $2000... When folks ask me what to get, I tell them to go to the store and handle both the Canon and the Nikon units. Buy the one that fits their hands best. See if one has a better eyepiece than the other. I've not mentioned the other brands because I'm not that familiar with them, and they are playing catch up to the leaders. Most of the pros I know of use the Nikon and Canon lines.

Don't get caught up in the megapixel race! If most of your prints are going to be 4x6s, 5x7s and occasional 8x10s, then, anything over 5 megapixel is going to suit you just fine. If you are frequently going to be shooting for 16x20s then 8 or 10 megapixels is going to work well for you too.

I said it was important to know what kind of photography you're going to be doing. If you are interested in action photography like football and soccer games then you'll want to take into account the number of frames per second (FPS) and the number of shots that the camera can store in a burst of shots. My Digital Rebel is good for ~3.5 fps. I'm interested in getting the new Rebel 40 D because it can shoot ~6 fps when I'm photographing horses and riders. The extra FPS help to be sure to catch all the action and expressions.
If you're mainly interested in shooting snapshots of friends, landscapes and some nature shots, then maybe you don't need the additional frames per second. There may be some other features that would drive me to the 40 D over the Rebel, Rebel XT, Rebel XTi, 5D, 20 D, and 30D, leaving the Mark cameras out because they are high end pro cameras costing $3-8K.

I'd say if this is your first DSLR, then it's probably a good idea to spend $800 to $1000 for the kit and see how much you are really going to get into it. After a while with the kit, you add some decent lenses and then work your way up the camera ladder, using the high end lenses I'll recommend later!

Next time... Books!