Seconding the PSW Study Hall and Shure resources and adding that Rane's web site (
http://www.rane.com) with their Pro Audio Reference, Pro Audio Book list and Tech Notes is a great reference. All sorts of good audio related calculators and convertors at
http://www.sengpielaudio.com/Calculations03.htm.
http://www.coutant.org/contents.html offers information for many mic models. You have to be a member to get the most from it, but
http://www.synaudcon.com/site/home.php has numerous useful articles, spreadsheets, tips,
etc.