If you highlight some text, you can just press a button to have it automatically emphasized on indented 4 spaces for a code sample. I think it would be great if we had this feature with strike-throughs so I don't have to manually type s tags. People use strikethoughs to delete text from their posts when editing it and adding information. This is nicer than just deleting it because it gets the point across that its older information but you can still see the original text.
In the absence of a button (and given that Jeff has said it's not likely to be implemented) you can use the HTML tag:
this or this or this
Like <strike>this</strike> or <s>this</s> or <del>this</del>
See this answer for a complete list of the HTML that's allowed.