This post on the Boston board http://www.chowhound.com/topics/348219 mentions
"My vegetarian girlfriend was a somewhat reluctant sushi eater, until she discovered the sweet potato tempura maki."
Another unique and addictive vegetarian sushi is Ume Shiso Maki. The tart flavor of the plum paste combined with the unique shiso flavor- yum!
Any other recommendations that might appeal to a reluctant vegetarian?