a question concerning early philosophical education

Along with building educational software, part of my new job is to put together short online educational resources. Mostly I'm doing this to make sure the software works well and to see where it needs improvement but also to help less tech savvy educators get their printed material into more interactive forms.

My new boss knows of my interest in philosophy so he recommended I build a couple short philosophical educational resources (content equivalent to maybe 10 pages in a textbook). So I'm looking for short topics that profs use for 101 type courses that every philosophy major gets to know fairly early.

The main subject I could think of was Hume's problem of induction. Can any of you think of others that might be interesting? Some epistemological ones might be fun, maybe color skepticism.

Another way to put this-- what early philosophical question had a big impact on you?