Lynn's are awesome!

If you're creative, there are lots of options...
Aquarium and reptile backgrounds
Fabric - lots of prints
Scrapbooking papers
Printed photos
Magazine photos
Drawings
Paintings
Wrapping paper

I use forest like aquarium vinyl cling backgrounds for now.

There's always the option of great stuff foam backgrounds or styrofoam backgrounds.

Is there any style you're looking for? Certain colors? Prints? Flat or 3D?