This site has a ranking of trinkets for mages based on build: http://wiki.shadowpriest.com/index.php?title=SimulationCraft/Trinkets/Mage. Kinda makes me feel better about having spent the 1000 gold or so it cost me to assemble a Blessings Deck for Phaedra's Darmoon Card: Crusade trinket.
(Link found in post 2903 of the TBC Mage Theorycrafting thread on Elitist Jerks.)
Edit: Of course, then there's further discussion about these results later on in the thread. I suggest reading it.