I’d always wanted to get started with Software Defined Radio (SDR), and I found this blog post which claimed you could get a USB receiver for only $20: http://sierrapermaculture.com/?p=357 I ordered one, and below are the steps I took to get started.
* Installed GNU Radio from source (needed to resolve a number of deps):
cmake ../ -DENABLE_GRC=ON -DENABLE_GR_FFT=ON -DENABLE_GNURADIO_RUNTIME=ON -DENABLE_PYTHON=ON
* Installed the rtl drivers/software by following these directions: http://sdr.osmocom.org/trac/wiki/rtl-sdr#Buildingthesoftware
* Installed the GNU Radio component: http://sdr.osmocom.org/trac/wiki/rtl-sdr#GnuradioSource