Sorry for the vague title--I don't want the title to be a spoiler.
I've seen the movie three times, and the last two times I looked specifically for clues to this question, but found none.
The final scene in Inception shows
Cobb's top spinning, as he goes off to be reunited with his children. The top continues to spin, then the movie ends, without telling us if the top topples--and therefore revealing whether he's in the "real world" or still in a dream. Do we know if he was in a dream at the end of the movie?
I'm assuming the answer is that we simply cannot know. But did I miss anything? Were there clues that I missed?