Strike-through text using the <del> tag.

OK, that was really easy. Here is a reference at W3Schools that goes into all the details.

If you are using WordPress you will find the del button on the HTML editor screen. Of course the editor button conveniently drops a date and time stamp attribute into the <del> tag as well, so the above line looks like this under the page:

<del datetime="2010-04-15T13:41:32+00:00">Strike-through text</del>

The ABC button of the visual editor uses inline CSS to create the strike-through effect. Here is an example of what the above line would look like under the page:

<span style="text-decoration: line-through;">Strike-through text</span>

To see an example of how strike-through text can be used feel free to read the latest revision of WordPress 3.0 Navigation Menu Styles.