Our magic sweet spot combo of tools includes 2 computers at each end of the pipe, one with VNC (a server at one end, a client at the other), and the other computer acting as "support", with iChatAV acting as our communications bridge, and various browsers and utilities handy on the non-shared screen. We leave an iChat video connection open, so we can communicate without having to stop editing source code to enter chat mode. This rocks nicely.
We had been using plain audio before, but Josh just got his iSight camera, so the open video line adds another dimension (and even without the video, the audio is much better - without needing headphones to kill the feedback loop). It could also come in handy, since he has a large whiteboard behind his chair, so he can sketch things up on it and I can see what he's drawing.
I never thought I'd be a such a fan of distance collaboration (although it has worked extremely well before) - it is always better to meet in person. But this combo makes it about as close to a face-to-face meeting as possible. Still not quite there, but pretty darned close.
One of the cooler things about the setup is that, except for the iSight cameras (which are entirely optional, but sure work nicely), the entire setup uses free software. Not necessarily Free Software, but no expense. This blows the doors off of Breeze Live, Centra, and any number of other "collaboration" suites.
We're seriously thinking of writing a paper, and/or presenting something at the next NMC conference on this setup.