Q: Hello. I have a Tacx turbo trainer and want to know how far I have covered, rather than time whilst watching tele in the garage any suggestions on a reliable rear wheel odimiter. Andy.
A: Hi Andy, well for a start a rear cycle computer is a great way to keep tabs on how many miles you are clocking up while on the trainer, and better of all it's another bit of kit to take your mind off pain!
There is a good discussion over at BikeRadar about this here. As you can see the general consensus is that you are better off getting a turbo trainer with a computer, rather than fitting one after - however if you got a normal computer and bought a long wire kit which are available, it might be a good option.

A cheap turbo trainer with a computer integrated is the Jet Black Dynometer Turbo Trainer