Codepen is totally free, but has a PRO version with more options like saving private Pens. The Codepen PRO service also provides cross-browser testing, pair-programming and teaching options for just $9 per month.
Embedded Pens, like the one below, are a great way to display working demos of your work. Any Pen can be embedded on any website. Just copy-and-paste the HTML embed code. Not only can you see the rendered result, but you can see all the code used to make it in a super-slick tabbed interface.
You also have complete control over the look of the Embedded Pens. With the integrated Embed Builder, you can quickly change colors and settings, even making them into a theme you can apply to multiple Embedded Pens. Or you can take complete control by applying your own custom CSS.
Embedded Pen Example: