I like the idea of interviewing family members...
I usually bring in my husband, in full military uniform and he spend the entire day with us (if his schedule allows). The kids ask him questions and he does really well with answering them, and fielding the not-so-good ones (Have you ever killed anyone? - he gets asked that every year). Last year the kids made card and we sent them to a friend who was at the time in Iraq who dispersed them to others over there. We even had a few write us back!
We also have a school-wide contest of which class can have the highest % of students wear red, white, and blue.