On what you need. The 1D I have is horrible above ISO 800, but bellow that I get very sharp images straight out of the camera. While only 4 megapixals, I have done 32x40 posters with it that look incredible. Also, beeing a CCD sensor, it has an electronic shutter which gives me a 1/500th of a second flash sync which is great for strobing sports. I mount studio strobes up high in gyms for basketball and that 1/500th gives me a great fall off of light separating the athletes from the backgrounds. All of the other Canons use a CMOS sensor, which is nice, but limits your flash sync and is not as sharp straight out of the camera. I like the 1D series and the 1Ds series, but if I had to choose a new camera, I would go with the 1D Mark III. But you have to remember too that these 1D's are huge and heavy cameras. More so in my opinion than the film EOS-1's. I know a bunch of car shooters that use a 5D over a 1 series because of size, still getting full frame sensor, and the cost is much lower. There will be a successor to it coming out in the near future, but you can find some place selling a new 5d for $2500 and lower. I have even heard great things about the 40D, but it has a very small sensor compared to the 5D/1Ds and 1D's.
Carl Auer - 82 FI X1/9 "Copperhead"
Seattle X1/9 member #50
Professional Photographer based in South Central Alaska