Bunnies! Bunnies! Bunnies!
I esp. love Michel & Co's Beatrix Potter stuff. VERY cute!

I haven't added to this in quite awhile but...
When I was little I started a "Whisker Box." It was just a small rectangular coffee can that I decorated with stickers. If I found a cat whisker or (in the case of Tinker) a baby tooth, I'd glue/tape it to a piece of paper, label it, and place it in the can.