Sangetsu is absolutely right about the airport limousine bus... and I don't want to complicate this but there are actually 2 cards that you can now buy in Tokyo. One is called Suica as we've been talking about - it is run by JR train company. The other one is called Pasmo run by the Metro subway company.
If you take the airport limousine bus from the Narita then in exactly the same way as JR has a deal on Suica that gets you a discount on the Narita Express, Pasmo has a deal that will get you a discount on the airport limousine bus. In every other way the cards are identical and can be used in exactly the same way.
I'm a Pasmo user because my home train line station is on a subway line. The deposit is the same and you can get it back in the same way when you leave Japan.
Hope it helps
