How should I exercise when I don't have x?

I've had to get creative about ways to get exercise into my day at a level that works for me. Anyone who has financial constraints, doesn't have sports at school, is in an area without good workout options, et cetera, has had to deal with this. So, I figured that we might have use for a thread on creative, inexpensive ways to get good exercise, especially with those contraints or space constraints. - Heather