well the 580 is the only master, but not needed unless you have more
than 1 flash (and doesn't matter if you have a 60D or 7D with their
built-in transmitters.


580 does full rotation, 430 and 320 only rotate 3/4 (apparently the
'wrong' way for portraits, but i'd try it in a shop if you can). 270 is
fixed.


430 and 580 can zoom to 105mm, and give AF assist grids, 320 and 270
only give wide/normal modes and fire the flash for af assist.


.


that's the main of it, otherwise you're paying purely for power. you
can always dial-down the power on a higher model, can't get more from a
lower model though. (2 smaller ones can provide for more interesting
studio effects though, if you're into that sort of thing)


.


http://www.canonrumors.com/files/580EXII.pdf is a fairly good idea to
read. if you don't understand the technical, just understand that
there's a chance you may have to send a warranty repair so don't buy
from Hong Kong or USA (i know it's cheaper though).


http://www.canonrumors.com/2011/05/r...n-flashes-cr2/
and http://www.canonrumors.com/2011/07/t...the-flash-cr1/ may
or may not interest you, but if you wait for 'the next new thing',
you'll be waiting forever and never buy anything. (actually, it makes
sense now, putting the optical flash controller in the 7d/60d/etc, if
they make a radio wireless controller, that'll be another add-on gadget
they can sell you...)