There are whole forums, and sites dedicated to discussing cameras, lenses, etc. DPReview springs to mind.
I'll make two comments.
1. The idea that you need a "fast" lens is, in my opinion, wrong. Ask yourself how often are you shooting below f4? Most of the time you're probably even shooting at f5.6 or higher due to the depth of field. What you need is a camera with high ISO ratings with low noise, and possibly image stabilisation.
2. The cameras I use are:
Canon S70 (small, portable, light weight, but full manual control)
Canon EOS30D with EF 24-105mm f/4L IS USM (39-168mm equiv)
From my limited experience with synths so far the two things I want are an external flash, and an ultra wide angle lens for better coverage of interiors.
Of course I also want a serious telephoto zoom for nature photography, but that's not really Photosynth related. :)
My Facebook wishlist for "My Camera Gear" has the EF 14mm f/2.8L USM and EF 300mm f/2.8L IS USM on the list.