Call Recorder - Records phone calls. Pro version supports other features.
Profile Flow - Create profiles to alter phone settings at certain times. Do things like turn media volume up when connected to certain bluetooth network or at a certain time (leaving work) turn off wi-fi, turn on bluetooth, media volume up. Lots of cool features and is simple to use.
Prey - Anti-theft app. Also is another app available for the desktop/laptop. A free account allows for 2 devices (i.e., laptop + phone)
Fing - Wireless AP analyzer. Great if you are IT, probably unnecessary if you aren't.
Google Rewards - Complete surveys for Play Store credit.