I just found a great little PHP utility called Markdownify. It provides a good PHP solution for those times when you want to convert HTML into plain text. For example, I often have clients who create newsletters through a WYSIWYG interface, and Markdownify can create the plain text version very easily. My current use for it is converting the HTML description of an event from an online calendar into plain text for use in an iCal feed.
In case you've never heard of Markdown... it's a plain text formatting syntax, which is very easy to read by itself, and which can be easily converted into HTML. Check out how it works here. There's a PHP version here.