Poster Street comes to us from the same people behind Certificate Street. Poster Street is a collection of free posters for classroom and office display. The collection is organized into seven categories. The categories of most interest to educators are Teachers, Kids, and Teens. All of the posters can be downloaded for free from Poster Street.
Try Easy Poster Printer to print the posters from Poster Street in large sizes.
Applications for Education
If you're looking for an inexpensive way to decorate or redecorate your classroom, Poster Street's posters just might be what you need.
Here are some related items that may be of interest to you:
Freeology - Free Printables for Teachers
Print Your Own Wall Size Poster
Free Posters and Slideshows from NASA