It's cmd-option left/right (shown in the navigation menu). Previously Safari used cmd-shift left/right which was rather bad, since that's select to begin/end of line (even in Safari forms). But starting with Tiger, Safari now use cmd-{/}. I could use these keys for consistancy, but probably in addition to the current.
I quietly second this. I have to admit that it bugged me a bit since the first time I used TextMate. I understand the conflict with the Apple-style text navigation (though I never personally use CMD to navigate -- I use PC-style home/end [fn-left/right]), but cmd-opt-left/right is too useful a keystroke to tie up with something which might just as well be the same.
In particular, I have always found cmd-opt-left/right to be far and away the most natural shortcut for virtual desktop naviation (with cmd-ctrl-left/right switching desktops and taking the foreground window with you). Having Safari use cmd-shift-arrow and TM use cmd-opt-arrow effectively prevents using *either* for virtual desktop switching.
Just a small frustration I hadn't mentioned before, but thought I'd raise since you mentioned optionally adding support for cmd-shift-arrow. It's fine with me if you keep both (as system-wide keystrokes like vdesktop switching override application shortcuts, anyway), though, of course. -jrk