Render HTML
Render HTML is a WordPress plugin which, at this point, simply converts all self-closing "singleton" tags within posts to unclosed HTML when displaying the post contents.
<img src="pic930.png" alt="930" />
becomes
<img src="pic930.png" alt="930">
WordPress: wordpress.org
Upcoming features will include translating all content in the WordPress database to HTML, and the reverse as well to made moves between XHTML and HTML more permanent.
Of course before that is added, there will be filtering to prevent XHTML-style markup from being saved to the database.
Currently any self-closing tags generated by the wp_head function are not filtered. I will be happy to add this as soon as I can figure out how it could possibly be done.
The work-around is to simply remove that from your theme header, which you've likely had to rewrite anyway if you're moving from XHTML to HTML.