I am unfortunately leaving Japan on August 3, 2010. I have a commuter pass (teikiken) for more than half (15 stations) of the Yamanote Line that is good through August 20. This adult pass is good from Ootsuka Station to Tamachi Station and lets the rider use it as much as they like, getting off and on as many times as they like, through August 20, 2010. Stations include Shinagawa, Meguro, Ebisu, Shibuya, Harajuku, Shinjuku, Takadanobaba, and Ikebukuro.
If you travel beyond these stations you will be charged only a minor amount. For instance, let's say you are staying in Shinbashi (Shimbashi) but plan to travel to stations like Shinagawa, Shibuya, and Shinjuku daily. This pass doesn't extend as far as Shinbashi Station. Normally you would pay about 190 yen each way to each of those stations from Shinbashi Station. With this pass you will only have to pay 60 yen each way.
Don't get ripped off by paying 37,800 (7-day), 61,200 (14-day), or 79,600 (21-day) for a Japan Rail Pass that you don't need if you are staying in Tokyo for a week or two this summer. This pass would normally cost 7,560 yen for a month. I am selling mine after July 30 for 3,000 yen, meaning it will pay for itself in just a few days. Email me if interested. I also have a child's pass covering the same stations for the same time period for 1,500 yen. Take them both off my hands for just 4,000 yen.