What's a good way to workout at home?

So here’s the deal. Where I live, its too hot to run or anything outside. The gym is too far away. I’d prefer to workout at home, in my (fairly large) room in the morning before going to work. I know I can do push ups and sit ups. Is there other good stuff to do?

Also, I’d like to get some cardio in somehow. Should I just do jumping jacks?

I’d prefer not to buy weights or anything else if possible, but if its not possible, I’ll do it.