I have requested these posters from The American Mathematical Society the last two years. They are great for your classroom! Get your Free Posters here.
Also, I found some other great ones you can print yourself that are Mathematical Moments, and are very current. You can find those Free Math Posters Here.
There are also Podcasts/MP3 files and web articles to go with it.
Then I found this site. You have to print your own, but if your library has a large printer, these would be nice to have. These have problems on them. Find the posters here.