So I have to admit, one of the most annoying parts of Beta testing my Death Knight is that I don't have access to any decent tabards. It's annoying, and I feel almost naked without one, but I don't have the time to grind exalted with any factions.
Thinking about that got me thinking about my tabard choices for my other characters. Of course, in Wrath, tabards are going to get all mixed up a bit, what with that new championing system, but I'll probably keep my favorite tabards on hand for swapping in when I'm not grinding faction. Actually, I may just tend toward my guild's tabard in Northrend, since our guild's backstory is intertwined with Northrend itself. Besides, I like to show a little guild pride when I can, and it's been a while since I wore a guild tabard on any of my alliance 70s.
Currently, my Druid wears the Cenarion Expedition tabard. Not only does the green and brown go well with his leather, but it's the closest there is to a Cenarion Circle tabard. For my Dwarf Hunter, it's an Argent Dawn tabard, since she's an especially zealous enemy of the Scourge. For my Warlock, the Scryer's Tabard, because he admires the Blood Elf race and (what he sees as) their dedication to knowledge at any price.
So why do your characters wear the tabard they wear? Do you plan to do any tabard swapping for Wrath of the Lich King?