Fuzzy flatid planthopper nymph (Hemiptera: Flatidae, from Iowa, USA). In addition to providing camouflage, it is thought that these waxy filaments defend against attack; if a predator only manages a glancing blow and gets a mouthful of wax, the hopper may have a chance to escape.
Masked Hunter - Reduviidae: Reduvius personatus (Iowa, USA). This assassin bug gets its common name from the tendency of its nymphs to camouflage themselves with detritus.
Well-camouflaged Buffalo Treehopper nymph, Membracidae: genus Ceresa (Iowa, USA). Membracids are most famous for their often bizarre adult forms, like the globe-bearing treehopper, but I find their nymphs to be equally charismatic.