Sorry, but I had to point these out, as the MER & Cassini calendars look awesome

http://www.ehartwell.com/calendars/

Philip

And these:
http://www.panoramas.dk/mars.html

I'm searching an educational poster showing the ringsystem around Saturn. Where to buy such poster?
Danke!

Well, there's a website in Germany selling those well-known posters:
http://www.wissenladen.de/catalog/index.ph...e48409e8cf4dbe0

Further I guess similar items are widely available via Amazon.com... but I would suggest to check the NASA NIX photo database or the media section at ESA.int where You can free-ly download high-resolution posters so You can print them via any online photo/poster service !