The US Postal Service offers some great program resources through their education program. It provides beautiful posters on specific topics and lots of integrated activities on the back. The one I just received is about the Hawaiian rain forest.
To get on their mailing list, write to
USPS Education Program
Att'n: Jean Schlademan
1735 N Lynn Street, Suite 5016
Arlington, VA 22209-6432
Include your name, address, grade, number of children, phone number and e-mail address (optional).
Sorry there is no email to contact - just snail mail!