I'm a lil' foggy on these, it's been awhile. But I got the endings where...
Chrono wakes up, and the entire world's population is composed of frogs.

Of course the ending where Lavos goes nuts and puts the world under ownage.

The ending where everyone goes back to where they're from. Then they show Magus flying around for no good reason.(Gay gay gay!)

When you beat the game without Chrono, and then the Princess (forgot her name, I always renamed my characters anyway) runs into the background.

The ending where they show a tree with leaves falling from it, then it turns to black.

And the ending that was of the games credits and that's it.

Oh, and the ending where thee King puts up a bell in the Town's Square.

Uh... I know I have seen more, but I can't think of them. I need to go play this game again.