An FM receiver is the first thing in every GRC tutorial. I just wish there was something useful that one can receive with one of these standard $15 RTL-SDR receivers that isn't super complicated or FM radio.
Granted, the absolute most common cases are out of reach with the cheap dongles due to frequency, bandwidth and encryption issues (i.e. ATSC, Wifi, Bluetooth) So they're not going to be terribly interesting to the average consumer but they are very handy little devices for hackers with any interest in RF.
[1] The default antennas they ship are not useful over a wide range of frequencies and/or for weak signals
But you have to be interested in the topics, find the right tools to decode what you're interested etc.
As an example: with not too much effort I've been able to listen and read a number of the temperature sensors around sending their readings. Then if you collect them for some period of time, you can try to analyze and process them to figure out how much of "noise" they collected (as if when they are mounted outside of a window and the window is open during the winter) versus the real signal (the outside temperature), and how many are completely broken etc, all based only on the data (e.g. when not seeing all the devices you record and when not knowing their placement).
It is fun for somebody who is interested in such kind of experiments (but not everybody considers such experimentation fun -- and then no tutorial is enough).
We live in the times where there are still unencrypted signals around. in some future, maybe there won't be anything to listen that would mean anything without the keys -- everything will be just encrypted noise.
https://github.com/antirez/dump1090