I use macros that put things together, including things like shield block and shield slam.
Now, while poor composition of these kind of macros can lead to sub-optimal cooldown/skill usage (Like Vene's example of Glyph of Blocking making your second shield slam far more worthy of cooldowns then the first) - good composition can free up buttons, and allow for quick reactions.
/cast [nomod:shift] Shield Slam/use [mod:shift] Gnomeregan Auto-Blocker 600/use [mod:shift] Coren's Lucky Coin/cast [mod:shift] Shield Block/cast [mod:shift]Shield Slam/script UIErrorsFrame:Clear()
This is the Shield Slam macro I use (I think, I'm re-creating this, since I'm away from my normal computer). Notice, that I have to make a choice (press Shift) to activate all my sweet, Shield Slam increasing cooldowns. The last bit keeps it from spamming errors when you don't have one or both trinkets equipped.
/cast [nomod:shift] charge/cast [mod:shift] intervene/cast [mod:ctrl] berserker rage
This one was born from a need to add charge and berserker rage to my layout in Defensive Stance. I now just target a mob, and press "F" (or whatever) to fly over to it, and then Shift+F to fly to yet another! If I was good, I'd add in a stance modifier to intervene in Def Stance, and Intercept in Berserker, but that hasn't come up yet.
I later added in Berserker rage, because I realized that this button had more or less taken the place of my old stance dancing / berserker rage -or- intervene macro, and it was just a decent grouping of abilities on one key in my mind.
/cast [nomod:shift] taunt/cast [mod:shift] mocking blow/cast [mod:ctrl] chalanging shout
"2" - Resist, Damn
"Shift+2" - Resist AGAIN, Damn!
"Ctrl+2" - Success!
If a mob is attacking someone it shouldn't, various combinations of one key let me make that not so.
/cast [nomod:shift] devastate/cast [mod:shift] devastate/cast [mod:shift] heroic strike/cast [mod:ctrl] devastate/cast [mod:ctrl] cleave
Low rage? Spam it for Sword and Board procs.
More Rage? Shift+Spam for added HS rage consumption.
Many Mobs? Ctrl+Spam for added Cleaving.
The idea of grouping abilities under one button just seems to work for me - I'm whatever brained. It may not for everyone, but I'd suggest trying it.
Together, we can reduce the number of buttons we push, without lowering the number of abilities we use, or sacrificing choice in when to use them!