Claudio Giuliani has designed an RTL-SDR based wide spectrum analyzer.
The code is available on AlterVista. Software prerequisites are a Linux box (no Windows/OSX version) with Gnuradio and rtl_sdr utilities installed. The spectrum analyzer program is a frontend GUI of rtl_power for spectrum visualization and control and is coded in Basic for Gambas (a sort of VisualBasic for Linux.)
Via RTL-SDR.com.