I've been playing with an open source PC based navigation and charting application provided by the fine folks at SourceForge. 
Yes, the application and the charts are free. 

The application is available at http://sourceforge.net/projects/opencpn/

Free charts for the US are available at http://www.nauticalcharts.noaa.gov/

Since OpenCPN supports the ENC format for electronic charts, most charts available for US waters are available for free.

Download the software and give it a try.