I like your Pennies for Pachyderms name. It's catchy and educational.
How about a poster of an elephant (either a whole one or just it's head, big ears and all) whose trunk gets longer as you raise money?
The poster could include fun facts about elephants like:
~ An elephant can grow as big as a school bus and weigh as much as 250 student.
~ An elephant's trunk has over 100,000 muscles.
~ Elephants cry, play, have incredible memories, and laugh!
~ Elephants have greeting ceremonies when a friend that has been away for some time returns to the group.
~ September 22nd is Elephant Appreciation Day. (who knew?!?!?!)
During the fundraising period, you could ask an elephant related trivia question each morning during the announcements and draw a winner from the correct submitted answers. Here's a link to Ringling Brothers and their "Pondering Pachyderms" page (another catchy title, btw):
www.ringling.com/cec/ponder.aspx