CNET has reviewed the Canon EOS-1Ds Mark III a 21.1 megapixel full-frame digital SLR with 5 fps shooting, 45-point AF system and 3.0-inch LCD display with Live View.
They write; “The 1Ds Mark III can capture beautiful, amazingly detailed images. Colors are extremely accurate and, as mentioned above, the automatic white balance system does a great job of keeping color neutral across a wide range of lighting. One of the nicest things about the 1Ds Mark III is its low noise. You can make pleasing prints across the entire sensitivity range of this SLR, which is a liberating feeling when you’re out shooting. The Canon 1Ds Mark III isn’t for everyone. You really have to have a need for a lot of pixels to warrant buying one instead of the 1D Mark III, which offers very similar image quality, an extra stop of sensitivity, and double the burst speed for thousands fewer dollars. Ultimately, you have to ask if you’ve been disappointed in, or felt limited by, the 1Ds Mark II’s performance and image quality. Of course, the 1Ds Mark III’s larger screen, live view shooting, and beefed up AF and exposure systems also give a reason to step up, though these aren’t as big a motivation. Overall, I’d go for the upgrade, especially if it can be considered a business expense.”
The Canon EOS 5D features a 12.8 megapixel Sensor (full frame), AF with 9 points, LCD of 2.5 inches, Magnesium body, DIGIC II and USB 2.0. 
The Canon EOS 30D is an upgrade of the Canon EOS 20D (same 8.19 megapixel CMOS sensor) with a larger 2.5 inch LCD (230,000 pixels) with ISO up to 1600 (in 1/3 stop increments), Spot Metering and High Precision 9-point AF system.
The Canon EOS 400D (also known as the Canon Rebel XTi) featuring 10 megapixel CMOS sensor with improved microlens array, fill factor and lower noise, EOS Integrated Cleaning System including: Anti-static coatings on sensor surfaces, Separate low pass filter with ultra-sonic vibration, Software based dust mapping / removal.