I have collected many tier pieces throughout the years and other items that may go along with sets, I can never sit still with transmogrification, once I see someone wearing the same set as me I go and farm up a new one. So here are some of my transmogrification sets, feel free to use them if you like, I rarely go back to them:
Lawbringer Set
Got this set at 60 when I was holy, just seemed to be for a holy paladin for me.
Judgement
Got this set again at 60, along with scrolls of the binding light which is still in my bank!
Avengers Battlegear
Got this set a little later on because of the rep grind, think it was end of TBC, start of wotlk
Justicar
I got all the parts of this set. Still trying to get the boots from ToC for it, working on a matching shield and weapon.
Crystalforge
Got the entire set, not my favourite looking one though also obtained the shield in Gruuls lair but sold it for bank space
Lightbringer
Probably the second most common, after judgement set. Use the helm a lot with different sets and I like the shoulders, don't like the rest of the set that much so sold it for bank space
Redemption
Thought I would like it a lot more, but when I got it its not that great (black set). The yellow is nicer and I got the boots from Trial of the Crusader which sort of matches. I like the thick boots better then the clamped ankles.
Valorous Aegis
It's an okay set, never bothered to obtain the whole set, just helm and shoulders which I later sold for bank space. Don't like the dress
Turalyon
Nice set, had it for so long in wotlk, even the HC and upgrades look the exact same. Had the healing mace from ToC too
Lightsworn
Another set I had for a good while during wotlk, not a bad set but not great colours
Sapphirum
Got both the normal and HC set, very decent set and fits the paladin stereotype well. I prefer the HC version, and used the shield from Sindrigosa and Hailstorm weapon from EoE
Immolation
Very nice set, got the full HC during cata and used this the longest. Shield - Flamebarrier from a TBC dungeon. Weapon - bethilacs sword and a mixture of other fire weapons / enchants. I use a chest piece of the Bethilac boss so I don't have to wear robes.
Others
I have used a mixture of other non set items such as Ulduar / Naxx 10m. I have tried the exalted set and wasn't really my taste. I prefer sets as they tend to have all matching pieces. I have loads of set items that have been removed (blues and greens) I had farmed both Dungeon sets 1 & 2 but sold them for bank space yet again and then they were removed and set as DMF rewards, damn. I have the Zul Gurub set from the 60 raid, mostly a non transmog items such as trinket and ring, also the AQ 20 set (cape, ring and sword). I am trying out more non-set items but can't find a set I really like. I also try to have one transmog for tanking, another for healing and a 3rd for DPS. ATM healing and DPS are both Firelands HC. I would lvoe to get the Challenge Mode gold set, and since I am a collector I eventually will, just need to find a decent group for it.