Energy Conservation Audits
If you want to be scientific about sealing the leaks in your home, you could have an energy audit done on your house.
A trained auditor comes to your home with sophisticated equipment to see where hot and cold air is leaking out.S/he might tell you how to fix uneven heat distribution, reduce drafts and other changes you could make to lower your heat bill. See http://www.home-performance.org.
You might want to check with your state energy office to find out about qualified auditors. (I know you renters aren't likely to get one of these, but nothing's stopping you from dropping a hint to your landlord, particularly if you're paying for heating, cooling and electricity.)