I know there is a 14 page thread on healing trinkets; however, it hurts my brain trying to transpose an opinion from a shammy, druid or pally into a priest theory, so I'd like to get a more focused discussion on trinkets specifically from Holy Priest perspective.
I'm finally almost epiced out, just need a few more badges for my Bishops Cloak, and I have yet to see prince or maiden drop a shard or justice. Other than that its my trinkets that I'm now turning to figure out whats best to keep in my bag.
Currently I carry the Bangle of Endless Blessings, Aussies Light Channeler, Lower City Prayerbook, Eye of Gruul. Most of the time I keep the Prayerbook equiped and trade of between EoG and ALC as they both seem about the same in the long run in terms of mp5 return, but I do like the fact that the EoG effect is passive.
On trash and a lot of Boss fights I have Lower City Prayerbook and Scarab equipped because they provide the most +heal.
However, for mana intensive bosses I find Alchemist's Stone and the Bangle to be irreplaceable. I use the Bangle in combination with Inner Focus early on when I know I am not going to be casting, i.e. Boss Transitions, Silenced etc. Later on in the fight I have a macro for whispering a feral druid for innervate. The combination of innervate and Bangles usually gives me over 7k mana.