I've used asciidraw.com [1] in the past for diagrams like these. I like its simplicity. Then for fun, if you have to email the diagram, use the shaky tool [2]

I've used asciidraw.com [1] in the past for diagrams like these. I like its simplicity. Then for fun, if you have to email the diagram, use the shaky tool [2] to convert it to an image. [1] http://www.asciidraw.com/#Draw http://www.asciidraw.com/#Draw [2] http://shaky.github.bushong.net/ http://shaky.github.bushong.net/