hi,
here is a little list of nice links.
hope someone will add some, so that it will be a good collection.
www.websdr.org -list of websdr
www.rtl-sdr.com -general rtl related stuff
www.sigidwiki.com -helps to identify radio signals
through example sounds and
waterfall images
www.mods.dk -modifications, repair
instructions and improvement
of HAM rigs, HAM modems,
radio scanners, etc.