I know Kyle is probably sick of hearing about cork.
Anyway, I like to use dark cork tiles for backgrounds. They are siliconed onto the back glass. They provide texture and a dark color contrast for plants. I staple, actually I push staples, into the cork to hold Java Fern and Java Moss on the cork. Eventually it fills in creating a "living wall". I've also used Bolbitus and Anubias attached to the cork. You can build terraces and caves with the cork. It also great for hiding filter inlet/uplift tubes.
For large tanks, it's hard to beat the look of simple black paint for the background.