I hate the fact that we can't talk about topics that people disagree on (politics, philosophy, religion, history, economics, etc.). Sure people disagree, but why can't we just have a nice, calm chat about it? Most people either descend into cable news tirades or have no clue and/or no views about the topics. That, my friends, is the problem.
Anyway, I find that it depends upon people I know and don't know. If it's people I don't know, I try to find out a bit more about them. Where they go to school, what they're studying, job, hobbies, and things of the like. Depending upon the person, pets can be good topics. If I know the person, then I just ask about things I already know about them - how's school, any interesting courses, how their jobs are, family, etc.