I have a whole drawer full! Some I have bought, some copied out of magazines, some I had to make myself (royal pain in the pattootie!). My favorite online source is Quilting Creations International at
http://www.quiltingcreations.com/
The Stencil Company is also great as mpspeedy said. I find it handy to have one of my square rulers handy so I can visualize just how big the motif will look on my quilt.