Made by Aardvark in Utah, these saddle covers are an old favorite amongst gnarlier riders. Stretchy Neoprene (AKA wetsuit material) conforms nicely to the shape of most saddles. Protect your nice saddle from a muddy or rainy ride, and add some cushion. Also aids in bike stealth for parking your fancy-leather-saddled ride in thief prone areas.
Waterproof, but the porous fabric will hold water like a sponge, so don't sit on it after leaving your bike out in a rain storm.