hmm, ay screen size for duals is never easy :S the only thing i could suggest is the 720x900 vertical spilt and have them side by side. If you end up with tri then luckily you can go with a 720x900 for your main and 720x450 for the two clones (720x450 will have the same aspect ratio as the full screen, only a quarter of the size).

top bottom splits will severely mess with your head methinks.. 1440x450 eek!! although I guess you could put your action bars either side and free up a bit of viewfield like that, but I wouldn't recommend it.

it get better when you get to 5 (evil glint in eye attempting to wrestle another into 5 boxing)

with 5 boxing on a lappy you can have 4 mini screens taking up just 360x225 leaving you with a nice 1080x900 screen for your main which doesn't seem quite so strange anymore. that's what i run when I 5 box on the go or abroad :P I'll try posting a pic soon so you can have a looksee.