What's a good key binding for tmux on OS X? The default tmux binding is ctrl+b, which is pretty awkward to hit on a Mac keyboard, because there's no right control.  C-a was the default in screen, but that's the default in OS X for going to the beginning of a line (my shell uses vim mode, but it's inconvenient when ssh'd to other machines).  You can't use alt as a meta key, and cmd+a is already used to select all text.

So - what are others using that doesn't override default OS X behavior that works well?
I've been using Ctrl+s for some time. It does not shadow any shell command I know of, and is quite convenient to hit if you also have CapsLock mapped to Ctrl (this can be done from within System Preferences->Keyboard->Modified Keys).