In AE 5.5, there was a wonderful plug-in called Fractal Noise in the Render category. Alas, in AE 6.0 it's gone. Gone from the Render category, that is. They moved it, and you can now find it by going to Effect>Noise>Fractal Noise.
If you're used to buying interesting background treatments (swirling colors and designs), you might want to put your wallet back in your pocket and introduce yourself to Fractal Noise instead. It's AE's one-stop -shop for all funky patterns and backgrounds.
Sure, it looks like Photoshop's Clouds when you first apply it, but dig a little deeper to mine gold.
Play with the different effects in the Fractal Type dropdown.
Adjust brightness and contrast
Twirl open the Transform properties to find a slew of really cool properties that animate.
Hint: uncheck Uniform Scaling, and increase the Scale Width category to create water or wood-like textures.