Below, you'll find "The Internet Marketing Written Style Guide" from Hubspot. I read it today and think it's pretty good.
It's too easy to be complacent and not write concisely and clearly. I think this guide will help me out. If you're interested, go ahead and download it.
Disclaimer: I signed up for a 30 day free trial of HubSpot, two weeks ago. So, I want to be fair and say I'm impressed with the company's services. I'm learning about the value of inbound marketing. I would like our One Call - One Click service to effectively use soclai media, so I decided to learn about HubSpot integrated inbound marketing service. If you are interested, here is a link to a 12 min video.