When developing a content managed website, whether it be in WordPress or anything else, it’s always hard to remember to make sure that almost every element that can be placed in a WYSIWYG editor is styled correctly.
Generally, you will grab some Lorem Ipsum filler text or the like, drop it into the visual editor and then start adding a few styles, however the problem is that you can easily overlook some of the basic elements.
In my travels across the web, the other day I stumbled upon a great resource that takes the worry out of remembering what to style.
The website is called WP Fill Me and it is basically a generator of filler content that is design for the WordPress Visual (TinyMCE) editor. It allows you just select specify content types or just everything you can think of and spit out the code ready for you to paste into your WordPress site.
From there you can start testing all your CSS styles to make sure they are all correct before handing your site over to the client.
UPDATE:
Unfortunately it seems that this website no longer works. Fortuntely, WordPress themselves offer an XML file with filler content which you can import into your WordPress site to test. They can be found on the WordPress codex.