GPS has come along, but it depends what you want
Basic GPS will do most of the functions, but not all
My bottom of the range Etrex can display useful cycling functions: current speed, maximum speed, average speed, moving average speed, vertical speed, odomoter, trip odometer, time moving, time stopped, total ride time, elevation.
Other useful stuff including: OS grid coordinates, north indicator, sunrise time, sunset time, ETA destination, how far off course (never far because I use the GPS to navigate!).
(Quite a few other obscure readings that I've never bothered to check out!)
You can get more expensive GPS units that will also measure temperature, cadence, heart rate etc.
Apart from power output, I can't think of anything else that you'd want to measure when cycling!