What's to do in Tokyo later this year?

I’m just starting the second week of my new job, and it’s become clear that I’m going to have to go and visit my staff in Tokyo sometime in the next few months. I’ll only have a day or two at most on my own, but I’m interested in any suggestions that Dopers might have for things to do while there.

(I’ve actually been to Japan once before, but it was on a very strict schedule, and I didn’t get to spend any time in Tokyo at all.)

So? Suggestions?

It might help if you could be more precise on the date. For a good schedule of events, I suggest checking the Mainichi Shimbun online at: http://mdn.mainichi.co.jp/ and particularly check out the “Japanofile” column for listings.
It might also help if you could let me know what sort of things you are interested in. I’m an artist and I love going to art museums, so if it was me, I’d head straight for Ueno Park and head for the Tokyo National Museum, as well as some of the other museums in the park. Some people might be bored to death with this sort of thing.
But the #1 thing I love to do in Tokyo is go shopping. I want to purchase the whole country and take it home with me. I especially recommend the department stores near the Shinjuku train station. If you want to shop for electronics, forget Akihabara, head straight for Nishi-shinjuku (a few blocks west of Shinjuku station).
But for the best overview of the whole scene, I’d recommend you purchase the book “Gateway to Tokyo” (pub Kodansha) which has a load of great information. Amazon says it’s out of print, “limited availablilty” whatever that means.
And don’t forget the old travellers maxim, “pack what you think you will need, then take half as much clothes, and twice as much money.” Except with Japan, I’d take 4 times as much money.

Well, I have some flexibility in when I decide to go. (I should have made that clearer in my OP. Sorry.) It will almost certainly have to be before the end of September, but if I had a good reason (:)), I could push it a bit later.

Museums will be high on my list, art galleries, low.

Thanks for the suggestions.

Ah, well if you can pick, I’d try to pick a time when you can see a festival of some sort. Matsuri are my favorite thing in Japan. But I’ll have to check out when the upcoming festivals are happening. I’ll get back to you.