so many possibilities!
I love Bazzill Basics Cardstock with an Edge! There are sooo many colors and all different kinds of shapes and sizes. My (semi-local) SB store carries a ton of them and I have just about one (or two or three) of each. You can fold them, cut them, chalk them, ink them and they look beautiful as backgrounds on pages. They add nice dimension. I have a hard time not using one on every LO.
Added bonus: INEXPENSIVE!