I'd love a 5dMk3 but too be honest the price is just a little high, though I'm hearing good things about the camera. I found the old 5D2 to very problematic with focus unlike the old 5D which just seemed to nail it time and time again - static subjects that is.
I was thinking of a used 1DSmk2 as you can pick them up for around £1200 with a warranty which may give me a decent landscape and 'sportish' camera but I've never used this camera so I wasn't sure about the fosus accuracy, tracking ability or speed.
As for the 7D, it seems great but I've read on many forums issues with focus - reminds me a little of the old issues with the 1dMk3.
And, yes I could go down the Nikon D3 or D700 route as well. Both are great cameras - problem is finding them at a decent price and condition. But, I've more experience with the Canon (through work). I also used to own a X100 myself, though that had to go to many issues with sticky blades and focus issues (though when it did get it right it could produce some fantastic shots).
Now my head hurts .....