Online Writing Lab at Purdue University
Purdue University Owl: Audience and Purpose
An excellent resource for learning how to write effective and professional memos. Offers information on a basic plan, the parts of a memo, and necessary attachments.
University of Toronto (Canada)
University of Toronto: Engineering Communication Program: Memos
This site shows exactly how to write a memo. The site talks about the components to use: header, purpose, summary, discussion, action.