Going to Tokyo!

This weekend I'm going to Tokyo. I know two days isn't enough time, but I just got frustrated with the fact that I've been in this country for a year and three months and still couldn't take a two hour plane ride to Japan. So, we're gona do one of those crazy weekend trips where you leave at 1:30AM on Saturday monring from Incheon, get in to Haneda (Tokyo) at around maybe 3:00am then come back to Incheon at 3:00AM or so on Monday morning.

I guess we'll catch the first train into the city and our first stop will be the big fish market, since I'm sure it will be the only thing open in the city... and we can get some sushi (I have to eat sushi in Japan). From there, though, I have no idea what I'm doing. I was hoping someone out there could give me some advice on the TOP things to do in Tokyo for a weekend. Is there anything you suggest, or just as useful, DON'T suggest? Also, if anyone has a suggestion for hotels, let me know. I want to stay in a ryokan if possible, just because they look cool, but I also want cheap though too... so... yea.