I have a very basic specialized - I think it's called the speedzone elite. It's wireless, very reliable and provides all of the basic mileage data (average speed, odo, miles per trip, etc). It replaced a very unreliable cateye wireless (don't like to worry about the wires...I kept having them break)

I've also heard good things about the basic sigma, but don't know for sure.

If distance is what you want to make sure you have, the simpler the better IMO