So, do you guys know about RTL-SDR?
Basically it turns cheap DVB-T-Sticks into a Software Defined Radio with a frequency range of 52-2200 MHz / 24-1766 MHz (depending on tuner).

You can do some cool stuff with it, like getting images from weather satellites or listening to unencrypted voice transmissions (e.g. pilots talking to ground stations etc.)

A compatible DVB-T-Stick costs $10-$20, so it is really cheap for what you can do with it.
You can find more information (and more possible use cases) on rtl-sdr.com.

I attached a screenshot showing the position, speed, altitude, etc. of nearby aircrafts by receiving ADS-B signals at 1090 MHz using my Terratec T-Stick Plus (with E4000 tuner). I can receive transmissions from planes that are up to 120km away from me using the supplied antenna.

Yup, I have one such stick as well, also from Terratec and based on an E4000 chip, and once in a while, I do listen to unencrypted voice transmissions (among other things) as well
But the ADS-B signals I receive are usually pure garbage (or so says the decoder program I'm using).

Looks like a cool little device to have, especially the pilots talking to ground stations part

Ha, that is kinda cool! ^^

I didn't notice until now that that was germany

The dongles, and RTL-SDR, work in every country

I thought that, but then again you are supposed to notice your own country you live in