Monkeys masturbate, and will also pleasure themselves orally.
Elephants pleasure themselves by rubbing against rough surfaces and by using their trunks. Elephant penises are shaped like an "S".
Porcupines have been observed not only masturbating, but also using objects, such as sticks, to rub against or ride.
Male African ground squirrels masturbate to ejaculation, and then consume their ejaculate.
Turtles will rub against rocks, bricks, or walls and emit a squeak-like sound of pleasure.
Walruses are very flexible and will pleasure themselves both manually and orally.
Ever see a bird rubbing its rear end on anything? Yup, birds masturbate too!
Male horses rub their penises against their stomachs for pleasure, while females will lift their tails and rub against trees and walls. Females will mastubate to orgasm and produce a type of ejaculate upon orgasm.
Dogs and cats masturbate. They will also show dominance by pleasuring themselves.
Moose can reach orgasm by rubbing their antlers against trees, and can reach orgasm as many as 50 times a day!
These are just a few examples, and I haven't begun to touch the odd sexuality of animals.
With all these great "side effects" of masturbation, I challenge you to give me one good reason why you should not masturbate.... Don't worry, I'll wait....