Franchises i've gotten into because of Smash Bros:
Kirby
Metroid
Fire Emblem
F-Zero
Ice Climber
Yeah, that's a pretty good set.
EDIT: Also, seeing the Eggplant Man trophy in SSBM is what convinced me to buy Wrecking Crew when it came out for VC, a purchase that i am thoroughly satisfied with.
Monster Hunter: pissing me off since 2010.