[naner]

"Then at the end he sees his kids, but they're exactly as they appear in his dreams. The top continuing to spin just makes it more explicit."

Nolan was just doing that to mess with the audience. Yes, the kids were wearing the same clothes, but the top started wobbling right before it cut away. So the audience is left not knowing if he is stuck in limbo or not. It could be interpreted either way.

Anyways, an easy way to tell if you are in a dream without relying on a totem (in the movie's universe) is to look at an analog clock. The numbers appear upside down in the dream world. For some reason this was only illustrated once in the movie.

[pak]

I seem to remember some Batman cartoon where Batman realizes he's in a dream because letters shift around oddly while he's trying to read something.

Indeed, I remember from my own dreams that text and numbers behaves oddly (disappears/changes when you look around).

I've also heard this technique is used by lucid dreamers (http://en.wikipedia.org/wiki/Lucid_dream) to figure out that they're dreaming so they can begin to take control of the dream.