You can now have a SDR (Software Defined Radio) for $20! The dongle is receive only, but it can handle from 64 MHz to 1700 MHz. It works in both Windows and Linux.
The dongle is actually a USB DVB-T TV receiver that uses the RTL2832 chipset along with a E4000/FC0012/FC0013 tuner. The DVB-T is not supported in the US, but there are plenty on eBay and elsewhere. Here is a list of supported devices.
There is a pretty active group over at Reddit that has been helping each other out.
You can also follow our findings with SDR via the Wiki.