I have a computer with cadence on my road bike, and I really like having it. As a newbie rider, it has given me a sense of what gear I should be in to spin in a good "zone." As I gain experience, I find myself referring to it less and less on the flats, but I still use it for climbing. I use a Sigma "double wireless" computer, meaning that both the speed and cadence features are wireless.
IMO, it's a good computer and reasonably priced. Here's a link: http://www.sigmasport.com/en/produkt...punkt=features
I also have a Cateye Astrale 8 on my hybrid that has wired cadence. I prefer the Sigma as it gives me less trouble. The sensor on the Cateye gets out of place easily.