Business Letters

This page has proper forms of address:
http://www.factmonster.com/ipka/A0771340.html

This site offers examples of alternate phrasing for different situations and some examples of letters: http://esl.about.com/cs/onthejobenglish/a/a_basbletter.htm

This site shows samples of block and indented formats:
http://www.wisc.edu/writing/Handbook/BusinessLetter.html

Plain English : www.askoxford.com/betterwriting/letterwriting/?view=uk