Writing is a skill like any other. Some people are good at it; others, not so much. The thing is, if you want to succeed in business, you must learn to master the written word--or at least learn how to fake it.
You can fake it pretty effectively by bookmarking LetterWhiz.com, which offers free business-letter templates for a wide variety of situations..
The Business catalog covers everything from Accomplishments & Compliments to Termination/Warning. In Career you'll find sections like Cover Letters, Raises, and Resignation.
The idea here is to give you basic but professional-sounding content for any situation. Most of the letters are brief and to the point, no more than 2-3 paragraphs. And in most cases you'll need to fill in certain areas to properly personalize them. But at least you'll have, well, a template for what you need to say. You can expand and/or embellish as needed, using the provided text as a jumping-off point.
The templates themselves aren't Word documents or anything like that; they're just text you can copy and paste into your word processor, Web form, or the like. I like that approach; it's a lot simpler than dealing with downloads.
Although some of the templates are almost annoyingly terse, they should prove quite helpful to business people who have trouble expressing themselves in print. The grammar, content, and composition are all sound, so you can be assured of sounding professional in all your business communication.
If you've found another good resource for business-letter templates, be sure to share it in the comments!