i play an affliction / demo lock amongst other things, so dont talk about overcrowded ationbars. what ive done for all my classes is move from wasd aross one to esdf.

this leaves aqw which i usually use for short cooldowns, some interrupts, misc abilities or charge type mechanics. on my warrior for example Q 1 and ` are charge intercept and intervene.
2 is a taunt on all of my tanks.
R and T are main spam abilities, with 4 and 5 being the others.
for example on my lock r is shadowbolt, t is incinerate, 4 is soulfire, 5 is hand of guldan.
G and V are aoe abilities, for lock thats shadowflame hellfire or seed, for my warrior its cleave and shockwave, dk has blood boil. my pally has holy nova in there, priest has whatever her nova is.

next setup was shift ctrl and alt on r and t, but i put the actual buttons for them on the far right action bar.

and with all of that i still have raid markers set to F1 -F8.
and i have all the rarely used abilities, like the rarely used curses and stuff for other trees under the second pane.

sounds complicated but it works.

oh also i had to move reply from t to y, it replaces the acievements pane, but you dont need to check your achieves in a hurry in combat, and shift y works just as well.