I have to talk about an interesting Japanese-related topic in Japanese class

I think dialects in Japan are interesting. You can find many Japanese dialects.
http://en.m.wikipedia.org/wiki/Japanese_dialects

The Earthquake/Tsunami that happened a while back?

Body langauge. They have very interesting body langauge which are slightly different from other countries.

Like when they are referring to themselves, they point to their nose instead of chest area. And when they want to get pass a crowd, they wave their arm vertically up and down(in a chopping like manner?) There are many more. I saw a very interesting video on youtube on this before but I lost the link.

EDIT: okay this wasn't the one I watched before but hope it gives you some insight. http://www.youtube.com/watch?v=Mi6h8zktO1s

How about the history of bonsai or origami or the derivation of kanji form the Chinese? How about the beginnings of the Shinto religion?

You can talk about:

Japanese dolls
origami
some famous cultural festivals - white day, children's day, star festivals etc
Manners - like, you're not allowed to wear shoes inside
Robots - advanced technology