Well, AFAIK the best DSLR for under 2000$ is right now the Nikon D7000, at least if you want to buy new. Either way it has any feature a professional would demand from a camera. Thanks to being APS-C format, it can use the smaller and cheaper Nikon DX lenses. There soon will be a 2k$ FX Nikon camera, the D600, since it was just announced and will be just 100$ above the 2k$ barrier, initially. You always still need lenses, though, and FX lenses are more expensive than DX lenses, albeit there is also a lot more lenses to choose from and you can use even very old lenses, from
eBay or elsewhere. Some of these lenses will even still be manual focus.
I dont know what the equivalent from Canon would be, but its probably also quite good. Canon and Nikon offer an extreme number of lenses, including a large number of older lenses you can get from
eBay and elsewhere.
Pentax is a special company. Very old, and has nice features in their cameras like weather sealing, sensor based image stabilization etc. All in all not fully competitive to Canikon, but not too bad. Mind everything not Canikon has less lenses offered and these lenses might be expensive and inferior quality, too.
Sony is still quite young in the camera market and frankly all over the place. Not really fully competitive to Canikon either, though. And I think they have given up on DSLRs, they build mirrorless now. They just released a 3k$ mirrorless, the A99. Its a bit hard to explain to newbies why Sony isnt very successful with really high quality cameras. Basically they focus on making cameras good looking in magazines, instead of making cameras that are fun and practical to make photographs with. Sony is compatible with Minolta stuff and they recently bought Zeiss and since then get a lot of new Zeiss lenses, which are of excellent quality.
Panasonic has to be mentioned as well. They also do DSLRs. They are inferior in quality though. But do great video (just like Sony, Pentax and Olympus).
I am not aware that Olympus actually builds real DSLRs anymore. Back in the old days of film, they certainly did. And some time ago they had FourThirds, which are DSLRs with an even smaller sensor than APS-C. Because of lack of demand, these cameras no longer exist. There are also Micro Fourthirds now, which are the same sensor size, only mirrorless. There apparently isnt too much demand for these either now. Probably mostly because APS-C sensors are cheap as dirt as well now.
Sigma builds Foveron X3 stuff. First problem is, it has like zip low ISO tolerance. ISO 400 and higher will quickly give you quite awful image quality. Even some compact cameras are more tolerant. Also, these cameras kind of suck completely in every other aspect but just the picture quality itself. So no good autofocus or good build quality or anything like that. In short, great for landscapes, but dont try action (sports, children). The current DSLR is just at the 2k$ limit right now. It started at 10k$ a year ago. I dont know the lens quality, but I know everyone agrees the compact version DP1M and DP2M have awesome, perfect lenses. The DP1M has an 24mm equivalent and the DP2M a 45mm equivalent. Both cameras and the DSLR, of which the name escapes me right now, have the same APS-C sized 15.4 Megapixel Foveon X3 chip. This is full, real resolution, not emulated like with all other digital cameras (except the 3ccd ones in some video cameras).
Fujifilm had some years ago DSLRs, but they are actually compatible with Nikon lenses. They have now started their own brand of mirrorless APS-C cameras like the X-Pro1 or the new X-E1. There are only very few lenses to choose from so far.
I think thats all companies that offer consumer DSLRs - or no longer do so.