PicMonkey has a vast collection of impressive overlays and stickers. You can even upload your own!
Geometric, Hearts, Stars, Symbols, Arrows, Comic Bubbles
Labels, Paper Scrap, Pushpins, Buttons
Lips, Sunglasses, Facial Hair, Hats
Happ-icons, Critters Buggin', Ordinary Beasts
Roses, Floral, Daisies