Hmm....I can think of Kappa Maki, which is just cuccumber rolled with sushi rice and seaweed. And also Philidelphia Maki which you can substitute the whitefish for cuccumber and use lite cream cheese instead of full fat. Avacado makes a great sushi addative to substitute for fish because it has a great texture, a little oily a little sweet like some fish. Umm..if I think of more I'll be sure to add them here.
Ah, if you Google "Vegetarian Sushi" you get some good links too.