Canon Welding: He's managed to tie in almost all of his own personal property without even resorting to parallel dimensions (though those do exist in his works).
Catch Phrase: In all three of his urban fantasy series, he uses variations on "Needs must, when the devil drives" and "Suddenly and messily." And when I say variations on the first one, he's gotten pretty damn creative. Also, he loves to have his characters to use their over-the-top reputations to intimidate their foes.