Amorphophallus titanum bears the world's largest inflorescence at up to 8' tall. It is also one of the Holy Grails of the horticultural world. It's not easy to come by or to acquire and grow (mainly due to its size and preference for warmth.
A tropical close relative to our native Arisaema (both Aroids), Amorphophallis titanum, bears tremendous flowers - each up to 8' tall! The burgundy trumpet-collar surrounds a steely spathe which towers to 8 feet or more. Not pleasant smelling (pollinated by flies), this is a plant for the true collector and one with the space to devote to it as the foliage will top out 10-15' and is a broad parasol of divided foliage on an exotically mottled stalk.
These are young but sturdy plants, currently in 4" pots and around 12" tall.