I like the look of the link dialog here. It darkens the screen and is probably modal (although I haven't tested that I just assume it is). What's a quick and easy way of darkening the screen like that witha jQuery UI Dialog?
The functionality you're talking about is provided by the WYSIWYM Markdown Editor
To do it with jQuery UI's dialog, try this:
$("#something").dialog({ modal: true; });
<div id="something" title="modal dialog">
<p>Add your stuff here.</p>
</div>
It's not exactly the same by default, but I think it's even prettier. ;)