I recently installed a Cateye Atrale 8 on my wife's bike. I pointed it out to a friend before a recent ride and he wanted to know if it was wireless. The point is -- if you discreetly route the wires (at least on the Cateye), they're not very visible, IMHO. Having black cable housing helps, of course.

I used black electrical tape to hold the wires to the brake cable housing; running the wires along the backside of the housing so they're not visible from the front of the bike. I hold the wire in place with a strip of clear adhesive tape just behind the front fork, one midway on the downtube, and one at the bottom bracket. All the excess wire is coiled and held in place with a tie-wrap on the lower portion of the leftside chainstay, just behind the bottom bracket.