I was in Tokyo for a few days earlier this year as part of my trip to Japan. We stayed in Shinjuku at the
Keio Plaza Hotel which was pretty good and only a five minute walk from the station complex, (note if you go out of the rear entrance to the hotel and up the road directly opposite about a block there's a good noodle resturant on the corner

)
Night life seemed pretty reasonable, (in Shinjuku you really want to go into the area the opposite side of the station to the above hotel), and there seemed to be lots of bars and resturants. We wandered around Saturday evening and the area was packed with people having a good time, and unlike in some places here, you felt pretty safe despite being in huge crowds in a strange place. Can't comment on clubs though as that's not my scene.
Other things to do, well you have the
Meiji Shrine amongst others, (note that if you are going to go to several shrines then you can get a book and have it nicely stamped in each one). If you can stand getting up early then the
Tokyo Fish Market is good to see but you really need to be there 5-6am to see things like the tuna auctions ... after 6am the little sushi places around it tend to start opening and you can get some really good fresh sushi (mmmmm tuna ....). Note that you need to know exactly where you are going (we got lost for a while) and it's a bit dangerous as it's a working market and there's these little truck things zooming around you have to avoid.
But, or course, a trip to
Akihabara is a must for all the techie stuff.