Seen any good movies lately?
I'm reading <book>, have you read it?
My allergies are driving me crazy, how about you?
You could run through the alphabet (which you will always have handy) and pick a topic for each letter - allergies, books, cool, doctors, engines, famous, guys, heroes, idiots, joke, kin, library, etc.
What do you think of ... <scan the headlines>
Obama,
the guy who wants to burn the Koran,
the current sports scandal,
etc.
Conversational whiz words (look interested):
Really?
I didn't know that. (even if you did know that, let them tell you all about it)
What do you think I should do about ... <anything - school deadline, maybe>