I have to agree with all of the people posting sea slugs. Personal favorites of mine are Phyllodesmium poindimei, Nembrotha purpureolineata, Hexabranchus sanguineus, Dendronotus albus, Halgerda tessellata and Clione limanica.
Spiders (especially mirror spiders) are another group I find downright beautiful, as well as moths, bobbit worms, mantises, and peacocks.
Quick correction for the people mentioning albino peacocks - those don't survive past infancy. The adults you're posting are actually leucistic. Leucism is full pigment reduction instead of just melanin and is just the pigment switch for a cell turned 'off', hence why you can get piebalds, whereas albinism is a genetic defect rendering the animal incapable of making melanin. It's also where you get white lions and white tigers from. ^ ^