Writing Business Letters

10,000 Business Letter Templates English
http://www.insiderreports.com/resources/library/searchletters.asp

For dimensions see
P:\Letter Layout Standards

Templates for Word, Excel, Access, PowerPoint etc. (Thanks Ron T.)
http://office.microsoft.com/en-us/templates/default.aspx

Modèles de documents pour Word, Excel, PowerPoint etc. (Thanks Ron T.)
http://office.microsoft.com/fr-ca/templates/default.aspx

Plantillas Word, Excel, PowerPoint etc. (Thanks Ron T.)
http://office.microsoft.com/es-mx/templates/default.aspx