If you are planning to travel a lot in and around Tokyo a Suica card is a must have. You can get it at the same place you get a JR pass from if I'm not mistaken. It's a rechargeable pass. You can use it on metro lines, busses, vending machines, some cafe's and possibly also on other things. It really helped me out when I was there.
Suica - Wikipedia, the free encyclopedia
Japan Travel TV Narita Airport Bus or Suica Deal Express Train?