I've since read two of Ullman's books (PHP for the WWW and PHP 5 Advanced), the Powers books (PHP Solutions and PHP Object-Oriented Solutions), and Shiflett's 'Essential PHP Security' (the PHPSec guide is required reading also).
The two Apress Pro books ('PHP Objects, Patterns and Practice' and 'Pro PHP'), 'Essential PHP Tools', 'PHP5 Power Programming' (Andi Gutmans is a coauthor) and 'Advanced PHP Programming' by Schlossnagle are up next, although I'm currently working through SICP.
(Note: I switched to Postgres since reading Welling & Thomson; there are basically 10x as many MySQL books as PostgreSQL ones, unfortunately)
I'm bookish in how I approach programming too, and among your list have read "PHP & MySQL Web Development," Shiflett's "Essential PHP Security," and "Advanced PHP Programming" when I was first starting out (I started out as a PHP programmer). If you're anything like me, the books get less exciting as the knowledge they contain gets more familiar, which is inevitable among a certain class of books. I now read more language agnostic books on algorithms, math, and some broader concepts. We'll see how that goes.
Sara Goleman has a book on writing extensions for PHP that you might like if you want to 'cross the threshold.' These sorts of things can be useful to know how it all works internally, even if you aren't writing a ton of extensions yourself. The Schlossnagle book has a chapter on that. I'm not sure how much movement PHP internals have (I'm out of that world now).