http://www.libraryonline.com/default.asp?pID
=47 - At the Library Online, you will discover
the differences of the four styles of letter
writing; block, semi-block, indented, and
memorandum.

http://depts.gallaudet.edu/englishworks/writin
g/letter/writingletters.html - This site is useful
when you want some help putting together a
certain type of letter in addition to choosing
the style. Letter types range from personal
letters of apology to cover letters for
employment.