Gnome 3, omg, well. The thing I miss most is binding zooming in and out to keyboard shortcuts as is easily possible with Compiz, plus inverting the colors of single windows or the whole screen. At least the latter, however, is achievable without Compiz -- simply using:

xcalib -invert -alter

and binding that to a keyboard shortcut via the System Settings -> Keyboard dialog.

The same approach is, of course, also useful for older systems for which Compiz would be too much.