I recently helped a friend decide which brand to go with for a standard full frame body. As everyone has indicated, in about a months time the game will change with the expected 5D replacement. There's a chance it could be another affordable FF as was the case for the original 5D verses what I and a lot of other people are hoping for, a compact professional FF body, which is what you get with the D700 (sealed body and complete pro feature set). People are speculating that the pro version would be named the 3D and the affordable version the 7D.
If Canon goes the 3D compact pro FF route and if they can avoid producing a fundamentally flawed camera then it will likely one up the D700 (please take this with a grain of salt as just about any high end camera will produce exceptional results with a competent photographer, any differences in IQ will be marginal) and probably cost as much or maybe more than the D700. While if Canon goes the 7D route then the cost will be below and possibly well below the D700. They could also introduce both FF bodies. No matter what, it is your best interest to wait a bit.
However if you can't wait then Nikon currently offers the best bet for a FF body unless money is a huge factor then Canon offers a better deal with the old 5D, although, the D700 is definitely worth the extra $700. Compared to the 5D (the camera I currently own and LOVE) Nikon's D700 is exceptional with sensor cleaning, weather seals, frame rate, AF, etc. If it was me and the new Canon wasn't around the corner I would be all over the D700, it appears to be an absolutely wonderful package. Hats off to Nikon for producing it on the tails of the D3.
As others have mentioned lenses are a big factor, in fact, the better the camera and the better you become as a photographer the more important lens become in producing the kind of image you want. I am not talking about IQ but atmosphere and artistry, which for me is the only reason to pick up a camera. Nikon has great lenses and people seem to indicate that they will be rapidly modernizing their line up. Their 14-24 wide angle is so good that it is almost worth buying the D700 for that lens alone, although, for the body and that lens alone will will spend $4.5K. However, with the exception of the 14-24 I find that Canon provides me with the best lenses for my needs.
NIKON (suggested FF kit):
Nikon D700 $2,999 (newer and better in virtually every aspect)*
Nikon 14-24 $1,529 (wider and sharper)*
Nikon 24-70 $1,699 (no VR, expensive and heavy)
Nikon 70-200 $1,624 (comparable to Canon)
Nikon 50 f/1.8 $109 (cheap but not outstanding)
Nikon 105 macro $759 (very nice but expensive)*
TOTAL $8,719 to provide me with my preferred kit.
CANON (my current FF kit):
Canon 5D $2,299 (old and not that much cheaper than D700, wait for MK2)
Canon 16-35 $1,450 (not bad but not as good as Nikon)
Canon 24-105 $1,059 (the best all around FF lens, period)*
Canon 70-200 $1,100 (f/4 is insanely sharp, f/2.8 is probably comparable to Nikon)*
Canon 50 f/1.4 $325 (better but both manufacturers seem to struggle with their 50s)*
Canon 100 macro $469 (very good but lacks IS, unlike Nikon's with VR)
TOTAL $6,702 (that's $2,000 difference for the complete kit)
+Canon 85 f/1.8 is an outstanding lens, especially considering the price*
+Canon L primes: 35, 85 and 135 are the best of the best, although, I do not own them at this point*
Best,
Chad
http://www.witnesstobeauty.com