There's rumors about new releases on sept 9th. I think the imac will be updated in design before Christmas. Natural developments will be reduction of the "chin" underneath. I think they will remove the black band around the edge and make the whole machine aluminum, like the MBpros and cinema displays, with a white apple at the bottom instead of the black. They will look allot more Pro-ish and harmonize with the change of macbooks from black and white to aluminum too. They'll probably reduce the width of it again slightly and taper the edges similar to macbook air edges on back.
If they bring back matte screens too, it will be a very tempting machine.