How Do I Keep My Long-distance Relationship Alive?

I have been in this relationship for over two months now; he lives in Canada and I live in the USA, so we are about 500 miles apart. He’s coming down to visit me for about 5 days in July. Unfortunately we’re very limited during the majority of the year; we will be seeing one another for about 1 week every two months, and then I will have mid-May through late August living with him. This will be the case for the next 4 years (since he lives and works in Canada and I am going to college in NYC).
What sort of little things can I do to keep things going? We email often, and talk on the phone every day. We send e-cards sometimes. What other little things can we do to keep the relationship strong and just keep it from feeling strained?