This is a large overview... For purchasing in the US, I recommend B&H Photo or Adorama. I'm not from the US, nor do I live in the US; but I have some knowledge in the big stores in the US. This being the case, I can't mention many numbers, so I'm sorry about that. However, the B&H Photo, Adorama and Amazon have good standard prices.
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The best DSLR?
Currently at the head of the market is the Canon 1Ds Mark III, followed shortly, or on par, with the Nikon D3x.
Ten thousand, around there.
What you are asking is the best entry level DSLR, is it not? And yet if you aren't willing to pay, it's the best DSLR for your money.
I recommend sticking with Canon and Nikon, maybe Sony and Pentax, and definitely not Sigma or Olympus.
Sigma for its cameras, not its lenses, mind.
With the big four, excluding Olympus; Canon, Nikon, Sony and Pentax, are almost always available for mounting a third party macro lens.
I suggest the 90mm macro from Tamron, or the newly released 60mm that's coming out (Tamron). There's also the 105mm from Sigma. There are more, of course, but these are mainstream and only cost around $500~.
If you pick Canon, then the 100mm macro is your best bet. The 60mm is all right, but if you ever update to full-frame, you can't use it... but most people don't upgrade to full-frame, so...
Nikon has a few as well. Sony should have, and Pentax I don't know.
A quick search should bring up some results. From there, research. Search for the reviews, and the comparisons. The best third party lens is the Tamron 90mm. The Sigma is not as sharp as the Tamron. In fact, the Tamron is sharper than the Canon 100mm, which is unique in a third party lens.
Now on to the DSLR itself.
I suggest the Canon EOS 450D/ Rebel XSi. The XS/1000D is also good, but is not *quite* as featured as the XSi, although none affect photo quality except the small 2 megapixel range in between which doesn't matter, anyway. More megapixels doesn't mean better, and too many means more noise. I do *not* recommend the new T1i/500D, as it's just really consumer targeted and is not much better than the XSi in terms of quality. They've just boosted it up to 15 megapixels - again, I stress that it's a myth that megapixels make the image quality better - and added a video mode which can't even record at 1080 at 30fps; instead, 20fps. A video camera would be much better suited for video, at this stage. Canon makes their own sensors, and their CMOS sensors are incredible because they've poured money into research for their developments. Canon bodies don't have Image Stabilisation, but they have IS in quite a number of their lenses. Of course, this means you could be paying a considerable amount more for IS, especially in higher end lens models, such as enormous telephotos, but the good side is that you can view the stabilisation at work through your viewfinder. IS in-lens is also better because IS for a telephoto may need to be different than one for a wide angle. So it's customised to suit the specific lens, and in general provides more stabilisation.
If you want to go Nikon, try the D90, or for a cheaper price, the D60. There's a new D5000... but again, I don't suggest it. The D60, D40x and D40 all do not have an autofocus motor. They have a autofocus sensor of three focus points, as compared to most other DSLRs which have around 11 points (at entry level stage). The D90 is an excellent camera; slightly more advanced, but there you go - you won't outgrow it that easily and it's a good secondary camera. Whereas the D60/D40x/D40 could hardly be as without AF you'd have to buy specially maed (AF-S) lenses. Yes, it seems that Nikon is headed towards making all the lenses AF-S eventually, and all its entry level DSLRs without AF, it's still good so you can use other lenses from Nikon and third party lenses as well. Tamron makes some AF lenses to be compatible with Nikon, but these are limited. But Nikon's ISO handling is fantastic, with superbly low noise at higher ISO. Like Canon, Nikon has in-lens stabilisation called 'VR', or Vibration Reduction.
Sony; your best bet is the A200 or A300. I stress that the A350 is not worth it, and the 14 megapixels make the frame-per-second rate only 2. That's lower than many others which have at least 2.5. Mostly 3fps. Sony is not an inexpensive bran, and for their equivalent of 'L' series lenses, Carl Zeiss (although slightly better than the Canon L series), start around $1500 and average around $2000-3000. But you won't miss out on the image quality. After all, Sony makes sensors for Nikon. In built stabilisation means you can use any lens and of course it will be 'stabilised'. Again, it may not be as effective as in-lens stabilisation, but it works.
Pentax still provides excellent image quality; not so much as the others, but provides a good all rounder and is the best bang for the buck. Its advanced amateur camera, the K20D, is available for a considerably inexpensive price, compared to its rivals, and provides an excellent DSLR. The entry level DSLR, the K200D, is an excellent camera as well, and there is now a K-M, or K1000. This is not quite as good as the K200D, and for the price, it's recommended that you get the K200D instead. However, if you can't get your hands on the K200D, the K-M is still a good buy. All Pentax cameras have in built stabilisation, but again, this is not *quite* as effective as Sony's. But it does work, note.
Overall, Sony has the best image quality, Nikon has the best ISO handling, with lower noise, and Canon has the best in-between.
Olympus and Panasonic run on the 4/3's system. Currently, Panasonic only has two Lumix DSLRs, and use Lumix/Leica lenses. The Leica lenses, in particular, offer excellent image quality, but here note: the 4/3's system has troubles. It runs on the 4:3 ratio, like most compact/point-and-shoot cameras, and when you print at 6x4, for example, a small, tiny sliver is cropped out. This isn't much of a difference, but the focal-length multiplier, which normally on other APS-C cameras, which is most DSLRs up to the professional range (they tend to use full frame sensors), is around 1.5x, is 2x on the 4/3's system. There are also several drawbacks, such as the fact that you can only use 4/3's lenses and that everything is doubled. The aperture, if f/2.8, is really f/4, and the length is not 18mm but double that and so forth. I don't recommend it, but its not bad in terms of image quality.