If budget isn't a concern, the Canon 1D Mark III is an industry standard. I've been interviewing wedding photographers for a while and all the top guys use it. Prepare for spending a ton on lenses too. For mid-high-end, I'd go with the 30D and for more entry level, the Rebel. I have an older 10D (predecessor to the 30D) and I love it.

The Canon 1D is probably the best. You pay for the best though. I've been using the Nikon D80 for the last 6 months and I love my camera.