Of course there are many other kinds of sushi rolls. Get ideas for fillings by looking at the ingredients listed on a menu from a sushi restaurant. Also, try the fillings in different combinations. We mixed and matched, and almost any combination of fillings seemed to work. One person did not like the nori, so we left the nori out of a roll for her. If you do this, be sure to use enough rice and pack it tightly while rolling or it will fall apart.
To make Boston rolls, follow the California rolls instructions, substituting shrimp for crabmeat. To make lobster rolls, follow the California rolls instructions, substituting lobster for crabmeat.
Options: sprinkle sesame seeds on rice or add a light smear of wasabi before rolling. Substitute mango for avocado.
For inside-out rolls (rice on the outside) flip the nori over after applying the rice, so that the rice-side is down before filling and rolling.
The nori sheets can soften while preparing the rolls. I always prepare each roll from start to finish before starting the next roll.