The other day, a client asked me what to put on a sales or marketing one-sheet.
Again, like most other marketing materials, the first questions to ask when starting up a project like this are:
"What is the purpose of this piece?"
"How will I use it in my business?"
"What questions will people have about the text here, and how can I answer them?"
"What's the next step (and, usually, it's not buying the thing you're promoting!)?"
"What do they need to know to take that next step?"
Those questions will help formulate the content of the piece. Also, consider if you can even answer all of those questions in one or two pages – if not, another type of marketing piece might be better suited to selling the offering.
Then, ask yourself if you'll really give away a vast stack of one-pagers – if you can make use of the design and printing fee – or if you'd be better off doing this design piece yourself and printing it at home.
If you get past these questions, and still want to do a one-sheet, here's the must-haves for the content:
– Your logo
– Your contact information (don't laugh, people leave this off all the time and wind up having to clip or staple business cards to the one-sheet, which takes a lot of time and doesn't look terribly professional)
– Your Visual Vocabulary
– An attention-grabbing headline – address the problem that your reader's facing, or use some interesting words. 
– A call to action – what do you want the reader to do next?
– A way to get more information – reference to your website, a way to make an informational appointment, etc.
– All of the basic features of the offering – usually, bullets are a good way to communicate this
– The benefits – what will they get when they buy? What will it mean to them? How will it change their lives or businesses?
– If there's room, tackle commonly asked questions or your purchasers' objections.
– Don't forget to leave some white space on the page. If your document is too cramped and full of text and images, no one will want to read it.
And, before printing tons of one-sheets, be sure to run them by a "best client" and get their reaction. You don't want to print these up to find that they're not effective, or you've left out an important bit of information.