Garmin ForeRunner 405
I use a Garmin ForeRunner 405 GPS and heart rate monitor.
It’s a cool toy that keeps track of where you rode, how far, how fast and lots of other useful information. The data from the watch can be uploaded to a PC or Mac and the route is displayed as a route on a Google map.
I find it useful to see where I’ve been and find shortcuts and options for subsequent rides. If I’m going out for a workout the heart rate monitor keeps me honest. Here is a link to the manufacturer’s web site.