Look here first:http://sdr.osmocom.org/trac/wiki/rtl-sdr
Just follow the links from here - there are literally hundreds of pages.
Also, on Youtube there is/was a guy from Deutschland that had decoding software (for free) using RTL-SDR that you had to see to believe.
You can get these RTL dongles on ebay for (literally) just a few dollars.
I seem to remember the folks at DangerousPrototypes were doing a lot with these a couple of years ago.
I just checked ebay and there are 350 "hits" for "RTL-SDR." Most have the dongle, antenna, remote control and software in the $10 USD range.