http://www.davies.rowtech.btinternet.co.uk/ratemeters.htm - candence, ratemate
http://www.btinternet.com/~streamline/
http://www.nkhome.com/rp/speedcoach/speedcoach.html - speed coach and stroke coach
http://www.rowdata.co.uk/ - mini rate and solo
http://www.hastie.org.uk/nrc/ratemtr.html - how to use cycle computer
http://www.garmin.com/products/forerunner201/ - GPS system