The best replacement for power meter is heart rate.

The best alternatives to power meter are rated as following:
★★★★★  heart rate
★★★  aero wheels
★★★  cadence sensor
★★  computrainer
★★  spectrum analyzer
★★  heart rate training
★★  quarq
★★  heart rate monitor
★★  otdr
★  powertap
★  srm
★  new wheels
  spectrum analyzer power

Your alternative for power meter is not listed? Suggest!
Speaking about power meter, one probably shouldn't forget about strava.

Other search terms related to power meter and their ratings are:
★★★★★ strava
★ garmin 910xt
You have in mind a companion for power meter and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of power meter in all years. Click on graph for more.
power meter
heart rate
aero wheels