I remember seeing a guy who put 3 count 'em 3 handlebars on his Surly Big Dummy. It was ridiculous but intriguing at the same time.
I like the YAWYD Top Cap from Niner. It stands for You Are What You Drink and basically it s a mounting platform for your favorite bottled drink cap, say from oat soda or root beer or other fun time beverage.
There is also the MASH top cap:
MASH STOREROOM | MASH TOP CAP KILLING IT