Right off the top of my head, Sam Hain comes to mind.
He was the equivalent of a 'supervillain' during the days of The Real Ghostbusters cartoon, a pumpkin-headed demon that caused real havoc for the 'busters on a couple different Halloweens. His name is obviously a derivative of the gaelic festival Samhain (don't ask me how to pronounce it, it's
not pronouced as it looks), which is the equivalent of All Hallow's Eve in the celtic highlands.
I can't think of any other cartoon character with physical pumpkin traits, although indirectly related are the Headless Horseman of Sleepy Hollow and Jack Skellington, The Pumpkin King.