I love the Seal of the Pantheon because it frees up so many options for enchants and gems instead of just stacking defense rating.
My other trinket is my good old level 70 Commendation of Kael'Thas. The proc of that trinket, combined with Ardent Defender, has saved me on several occasions.
And after all, that's what tanking is all about, for me. Stack just enough threat to keep the bad guys away from your good guys, then pile on as much survivability as you can possibly get.
I would still like Essence of Gossamer
http://www.wowhead.com/?item=37220 to drop, but the Commendation
http://www.wowhead.com/?item=34473 is fine for now.
My problem with the epic trinkets is few of them have stats in addition to on-use or on-proc benefits. Sure the armor/dodge and parry ones are nice, but worth losing 57 (or 111) stamina? Stam works on all types of attack; armor and parry only work on physical damage. I guess for situational use (hi Patch!) they are nice to have.