I got to a store that had the old 27 model, and assuming the change of GPU does not affect the various sizes offered, here they are:
4:3
640x480
800x600
1024x768 (and also stretched)
1600x1200
5:4
1280x1024 (and also stretched)
16:10
1680x1050
1920x1200
16:9 (native aspect)
1280x720 (perfectly sharp pixel doubling)
1344x756
1600x900
1920x1080
2560x1440 (native)
(That last batch is full-screen, non-stretched modes: good for gaming! So Im glad there are a lot of options there. Eventually a game comes along where you must drop the res for performance.)