The problem with far too many sequels is that nobody bothers asking "why should we make a sequel" other than "the first movie made a butt-load of money!" There needs to be a reason to actually want to see a sequel. A Pixar movie I'd LOVE to see a sequel to would be "Monsters, Inc." Maybe with Boo all grown up, where Sully and Mike meet Boo's child.
Mark
I loved that Boo. I had a "nighttime friend" all through childhood which kept me from being afraid of what was lurking in my closet (the friend was actually streaks of light on the ceiling, shining through the hallway bannister from the light in our foyer; I named it Harvey). I loved how Boo called Sully "Kitty." She was a sweet character. And Steve Buscemi was perfect as the ratfink chameleon/salamander/gecko thing. He was twisted.