I've just bought a (wired) Cateye Enduro 8; £22 retail, probably a bit cheaper on the Internet. Easy to set up and seems to work well. After calibrating for tyre circumference it matched my car's odometer on a 4.6 mile test trip. I chose this model because, as well as the total odometer, it has two trip distance recorders, so I use one for the day's ride and the other for the distance on the current cycle battery charge. Also, when the time comes to change the computer's battery you can re-enter the total odometer figure and so keep the "total distance ever" figure going.