"BOMB ATTACK!" - Toon Link - Pull out bomb, jump-n-throw boomerang, then throw bomb.
"FINISH HIM!" - either when someone is at a high percentage, or when they can be chased off the edge (only if they're kinda far, otherwise i won't say it in time)
"SPIKE HIM" - when someone is below the stage in midair (and im not the one who got him there)
"SHORYUKEN!" - then usually followed by a - "HADOKEN!" - Luigi
"DIEEEEEEEE!" - When I fair or bair someone at a really high percentage.
"HERYAGH!!!" (or some other form of random battle cry) - when me and my opponent are both at a high percentage, and I use a potentially killing blow, whether it actually kills or not.
And my favorite one, when one of my friends is using Snake, and their enemy is at a moderate percentage, I yell - "QUICK! USE MY COMBO! GRAB-CHUCK-MISSILE!"