Have a blast man. I loved this one little bar in Ginza called 300 bar. Every and any drink is 300 yen, as well as the appetizers there. It's a standing bar only, but it's a lot of fun.
http://www.300bar.com/english/
If you see Yukari there, tell her Sean says hi from Arizona, haha.
Also, you should try to visit an onsen or sento. I regret not going to one during my week stay in Tokyo.
Check out the top of Sunshine City in Ikebukuro. You can take an elevator to the 60th story and get some great views. I think it costs about 700 yen to do that, and it was worth it both times I went. Go up at night for some breathtaking cityscapes and great photo ops with all the lights on the buildings. I think there's better views from some places in Roppongi, but I never made my way over there.
Next door to Sunshine City is Ikebukuro's flagship Tokyu Hands store. On the 6th story, you can go to Nekobukuro, which is a small cat petting zoo. I think access is also about 700 yen. Regardless, Tokyu Hands is a fun store you should check out.
Try your hand at Pachinko and watch your money go bye-bye. I didn't have much luck with the Eva machines.
If you see another foreigner (gaiKOKUjin, don't use gaijin, it makes us look even worse!) and they ask you how to get somewhere on the JR train line, tell them to just take the "Yamanote Line and get off at the last stop!" (If you don't understand it, the Yamanote Line just goes a huge loop in the middle of Tokyo and never really has a terminating point. A very horrible thing to do to a fellow gaikokujin, hahaha!)
Exit the JR station at Shibuya and check out the crazy 6-way intersection, one of the world's busiest crossings. I'm sure you've seen it in Lost in Translation and countless other movies. Give Hachiko a pat on the back for me!
Eat a delicious crepe at one of the many stands in Shinjuku. I had the strawberry cheesecake one and it was soooooooo good! Also, shabu-shabu anywhere is a MUST! Look it up if you need to. I went to the one inside Sunshine City near Namjatown.
Also, drink some Chu-Hai (
http://en.wikipedia.org/wiki/Ch%C5%ABhai) for me at each train stop. It isn't very potent, but it sure is fun to drink one at nearly every station and get wasted off of 5 or 6 of em. I like the Ume (Plum) one the most probably.
Hmmm, what else ... I'm sure I'm forgetting something, but there's just so much to do. I haven't been to Fukuoka, but my friend's wife is from there and I'd love to visit there someday. As someone previously said, they're the ramen capital of Japan, so you gotta get some there for sure!
This is the book I found most useful for sight seeing. Definitely try to pick this up before you leave.
http://www.amazon.com/Lonely-Planet-Tokyo-Encounter-Yanagihara/dp/1740595580
Also, try to pick up a small translation book as well. I found this small one extremely useful.
http://www.amazon.com/Rough-Japanes...=sr_1_1?ie=UTF8&s=books&qid=1216640357&sr=1-1
Oh, and this is the ONE THING YOU ABSOLUTELY MUST TAKE WITH YOU BEFORE GOING TO JAPAN. Take a small pocket compass! TRUST ME, it will come in very handy when you're trying to navigate Japan on foot and you're using a map. I was so disoriented before I bought one over there.
Also make sure to make copies of your passport and US ID, and put them with your luggage/carryon, in case you lose your real passport. It might help to print out some of our suggestions from here, because when you're over there, I guarantee you won't remember everything we suggest!
I'm jealous man, have a blast! I definitely cannot wait to apply for the J.E.T. programme after I graduate this year.
Edit 1:
Ahhh! I forgot! Go to Asakusa for a little more relaxed part of Tokyo. Check out the Senso-ji Temple.
Also check out the Tokyo Amusement Dome for a lil' theme park fun!
It's a bit rainy when I went last month, so check the weather before leaving and pack a light jacket to keep the water off of you. I'd suggest buying a cheap umbrella over there instead of taking one with you. Gotta keep some space in your luggage for bringing stuff back, right?!