So you guys think a Metro Pass will be sufficient? I don't know how much of a hassle transfers are, but if I don't need to use the Oedo line then I'll stick with just using Tokyo Metro. If I need to use JR lines I'll just pay for it (was planning on going to Kichijoji and Yokohama).
Buy Suica or Pasmo, which are good on virtually all underground and overground rail lines in the Tokyo-Yokohama-Chiba area.
They are not passes, but they are debit cards, like London's Oyster Card, that calculate your fares and transfers for you.
You don't save any money, but on the last trip, I liked being able to transfer between JR and the subway simply by swiping my Pasmo card, instead of the old routine of digging out a different card or stopping at the ticket machine.