I considered the neoprene covers, but yes their prices are rather high. So I went for a far cheaper solution involving a welly sock and a pair of scissors
And the bonus here is you can use any colour sock you want! And you've always got spare cover too!
Though I'll admit mine was more from a side of wanting to dull the shiny whiteness of the lens rather than "protect" it as such. I think careful use and always having the lens hood on is a significant move toward protecting the gear from general wear and tear.
Tools of the trade: Canon 400D, Canon 7D, Canon 70-200mm f2.8 IS L M2, Sigma 120-300mm f2.8 OS, Canon MPE 65mm f2.8 macro, Sigma 150mm f2.8 macro, Tamron 24-70mm f2.4, Sigma 70mm f2.8 macro, Sigma 8-16mm f4.5-5.6, Raynox DCR 250, loads of teleconverters and a flashy thingy too
My flickr