Sunshine City - You can observe Tokyo from above. Perhaps the most unique elevator ride on the way up to the observation floor - You'll know what I mean, if you go.
Seibu Mall - World's largest, or second largest mall.
Kubukicho - Red light district. It's massive. If you have Bon Jovi's hair style from the 1987, you'll fit in just fine, the chicks will love you.
Sony Building - Somewhat interesting. You can see and test out lots of existing and up coming Sony products. It's worth a cruise through, but don't waste a lot of time there.
Toyota Store - I can't remember where it is exactly, but it's a massive Toyota store (dealership), but not in the traditional sense. It's something like 7 storeys and has many interactive displays. Perhaps, someone who knows what I'm talking about will pipe in and tell you where it is.
Tsukiji Fish Market - Something that I didn't see, but mentioned by others all the time. Apparently, the best time to be there is 5am, which is probably the reason why I didn't go.