What are some good cardio workouts?

I moved to an apartment in the city and there aren't a lot of good places to go running, so I've been trying to find some good cardio workouts that will help me to keep the body fat off of me. I'm sort of tight on funds, so a gym membership and expensive workout equipment aren't really an option either. What are some good workouts that I can do around my apartment? Any help would be greatly appreciated.