Well there are several characters that are important enough to add that aren't in the characters section yet. They are:
Doctor Fish
The Dirty Bubble
ManRay (MM and BB III will be on the DVD coming out this month)
Lou (ice cream man/ balloon fish/ store clerk)
Mama Krabs
Don the Whale (whale that lifts weights with Larry)
Bubble Buddy
Redge (or Reg don't know spelling)
Doodlebob (evil doodle)