Snake Utilt. No explanation needed.
Meta SL. Again, no explanation needed.
Bucket is indeed powerful, but again situational and I believe this is more of an all arond kind of thing.
One that no one has mentioned so far is Marth's UpB.
It is INSANELY fast (see frame data below, I use it to stop a chaingrab from my buddy's Falco), has great knockback if close, use out of shield, use out of dash, and can stage spike like no other. When you're having off the stage fights, recovery is also important and bar getting caught on the bottom of FD, it can easily get you back on the stage, not to mention its vertical velocity is unreal and you can ledge hog quickly and hit an opponent off the bottom at the same time.
And just for ****s and giggles... Ganon Dair. ZZZZT! Thunderstorm!
Dolphin Slash Frame Data (Pulled from the Marth boards, thanks Steel2nd)
Invincible frames: 1-5
Hit: 5-11
Landing Lag: 34
Shield Stun: 13