I thought i share some of the macros i use, i developed them myself and found them extremely useful.
#showtooltip
/cast [exists,harm] Hemorrhage; Fan of Knives
#showtooltip
/startattack [exists,harm]
/cast [exists,harm] Backstab; Fan of Knives
These macros are for pvp, when you are spamming your main ability like mad and you lost target for some reason, (rogue vanished, mage turned invisible, hunter feigned death) these will cast fan of knives right away automaticaly.
Update: As Mannmedkniv suggested I added the /startattack command to the backstab macro, that way when you cant manage to land a succesful backstab you will cause some dps at least.
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#showtooltip Sap
/cleartarget [nomodifier]
/targetenemyplayer [nomodifier]
/cast Sap
This is a spammable macro when you notice there is an enemy rogue nearby, it will target the rogue and sap him even if you are currently targetting a further enemy, it ignores pets as well. If you want to sap your current target you hold down shift or ctrl or alt no matter wich and it will sap your current target. Place this on your default action bar in stealth mode.
#showtooltip
/dismount [mounted]
/cast [target=mouseover,exists,harm,combat] Blind; [combat] Blind; Stealth
Place this macro to the same bind as the previous one but in normal stance (no stealth), useful when you see a rogue while you are mounted. If you spam its key then you will turn stealthed then sap the rogue, if he gets you first then it will blind him. This macro also works for jumping down from your flying mount stealthed, which is a very usefull thing in many situations. In combat it also works as a default mouseover Blind macro but you can simply blind any1 with this as well.
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#showtooltip
/cast [combat] Vanish; [nomodifier] Stealth
This is a simple vanish macro, probably most of you have something similar, it saves you from wasting your vanish when you would come out of combat anyway.
/cast [nostealth] Every Man for Himself
/use [stealth,modifier:shift] Mind-Numbing Poison;[stealth] Crippling Poison
/use [stealth,nomodifier] 16
/use [stealth,modifier:shift] 17
/use [stealth,modifier:alt] 18
/click StaticPopup1Button1
Replace every man for himself to /use *your pvp trinket* and replace poisons on demand!
This macro only makes sense if you put it somewhere else then the default action bar, if you do so it saves you 3 slots. When you are stealthed you would not use your trinket anyways so when you are stealthed and hit this macro it applies crippling poison to your mainhand, if you hold down shift it puts mind numbing on your offhand, and if you hold down alt it applies crippling poison on your thrown weapon. It also handles the pop up questions. When you are out of stealth it works as a simple pvp trinket.
#showtooltip
/cast [nomodifier,party] Tricks of the Trade; [nomodifier] Cheap Shot
/cast [modifier:shift] Slice and Dice
This is another 3 in 1 macro, if you target a friendly player in your group it casts Tricks of Trade on him, if you hold down shift it casts Slice and Dice otherwise its a simple Cheap Shot.
/targetenemy [spec:1]
/targetenemyplayer [spec:2]
This macro targets the nearest enemy player and ignores mobs and pets when you are in your pvp talent spec, and targets the nearest enemy no matter if its a mob or player when you are in your pve talent spec. Bind this to your tab key! Swap spec 1 and spec 2 if your pvp spec is on the first talent panel and pve on your second.
I hope at least 1 or 2 of these macros were helpful for some1.