Pitbull - Everyone
Dominos - Everyone.
DMB + SpellTimers - Only the main uses this.
MSBT - Only the main uses this.
Cartographer/Chinchilla/Gathermate {Data} - Everyone uses Cart and Chinchilla. Gathermate is only loaded for those gathering stuff at the time.
Altoholic - Everyone
Fubar + Broker2Fubar - Everyone.
NQuestLog + Lightheaded = NQuestLog on everyone, Lightheaded only on my main.
MoveAnything - Everyone.
OmniCC - Just my main.
Postal - Just my main.
Prat - everyone.
Silver Dragon - Just the main.
Smartbuff - Everyone.
Rating Buster - Everyone
SpamMeNot - Everyone
SuperDuperMacro - Everyone
TipTop - Everyone

I don't have any DPS mods...if I care, I run /combatlog and plug it in to World Of Logs. I have no threatmeter, Pitbull shows threatbars/% based off the ingame threat for when I need to know. Some of the stuff is more fluff than anything, I could box without things like TipTop and SilverDragon, but anything that gives me more information with fewer places to look is a must-have to me.