I decided to list them by level, since that's probably the easiest to follow. But if you're looking for shields that drop in a certain location just push ctrl+F and write the abbreviation e.g. WC, BFD, BRD, AH (Auction House that is) and etc. If you're looking for a certain boss drop just write the name of the boss. Remember that quest reward shields usually are obtainable at low levels although it requires you to do a higher level instance, which means that even if you can take the quest for the shield at level 20, you might have to be several levels higher to do the quest (depending on how boosted you can be).
- Shields with mostly caster stats not included (although some of them are ok for tanking).
- Shields from heroic Outland instances not included, since no one does them anymore.
- Shields of green quality not included (since they're generally not very good).
- Shields from raids not included.
- Shields from PvP rewards not included.
- Shields are all of blue quality unless stated otherwise.
15 - Gold-plated Buckler (DM, Miner Johnson (Rare))
16 - Kresh's Back (WC, Kresh), Worn Turtle Shell Shield (WC, Kresh), Commander's Crest (SFK, Commander Springvale)
17 – Darkshore Warder's Shield (Quest, The Battle for Darkshore (horde)), Shield of Azsharan Conquest (The Conquest of Azshara (alliance))
19 - Redbeard Crest (AH, BoE)
20 – Shield Against the Evil Presence (Nightmare of the Deeps (horde), Blackfathom Villainy (alliance))
24 - Thermaplugg's Central Core (GR, Mekgineer Thermaplugg)
25 - Shield of Thorsen (AH, BoE)
26 - Resplendent Guardian (AH, BoE)
29 – Shield of Comrades (Quest, Stripping Their Defenses (horde)), Shield of the Righteous Cause (Quest, The Only True Path (alliance)).
33 - Skullance Shield (AH, BoE)
35 - Battered Viking Shield (Uldaman, Olaf), Olaf's All Purpose Shield (Uldaman, Olaf), Aegis of the Scarlet Commander (SM Cath, Scarlet Commander Mograine)
36 - The Green Tower (AH, BoE (epic)), Shield of Maraudon (Maraudon, Princess Theradras)
40 - Aegis of Battle (Quest, Venom to Undercity (horde only)), Savage Boar's Guard (RFD, Ragglesnout (rare)), Intricately Runed Shield (Scholomance, Ras Frostwhisper), Petrified Bark Shield (Dire Maul, Tendris Warpwood)
41 - Blackskull Shield (Ah, BoE (epic))
44 - Troll Protector (AH, BoE), Barrier Shield (Dire Maul, Tribute Run)
45 - Wall of the Dead (AH, BoE (epic))
47 - Stoneshell Guard (BRD, Roccor)
48 – Crest of Retribution (Stratholme, Ramstein), Husk of Nerub'enkan (Strat, Nerub'enkan)
49 - Aegis of Stormwind (AH, BoE)
51 - Rock Golem Bulwark (BRD, Panzor the Invincible)
54 - Skullflame Shield (AH, BoE (epic)), Avalanchion's Stony Hide (Azshara, Avalanchion)
55 - Draconian Deflector (UBRS, General Drakkisath)
56 - Milli's Shield (Quest, Shards of the Felvine), Avalanchion's Stony Hide (AH, BoE)
57 - Intricately Runed Shield (Scholo, Ras Frostwhisper), Darrowshire Strongguard (Quest, The Lich, Ras Frostwhisper)
60 - Jagged Obsidian Shield (Crafted (epic))
62 - Petrified Lichen Guard (Rep with Sporeggar)
64 - Shield of the Void (MT, Pandemonius)
65 - Shield of the Wayward Footman (AH, BoE)
68 - Platinum Shield of the Valorous (SL, Ambassador Hellmaw)
70 - Netherwing Protector's Shield (Quest, Ally of the Netherwing), Aegis of the Sunbird (Bot, High Botanist Freywinn), Ogri'la Aegis (Rep with Ogri'la), Silvermoon Crest Shield (SL, Murmur)
72 - Bulwark of the Tormented God (Quest, Ursoc the Bear God (level 73 req for alliance))
73 - Saronite Defender (AH, Crafted)
75 - Riot Shield (VH, Xevozz)
76 - Blade-Binding Bulwark (AH, BoE)
77 - Saronite Bulwark (Crafted)
78 - Bulwark of the Warchief (rep with Horde Expedition (horde only)), Shield of the Lion-hearted (rep with Alliance Vanguard (alliance only)), Leeka's Shield (CoS, Malganis Chest), Shield of the Iron Maiden (Blackrock Caverns, Rom'ogg Bonecrusher)
83 – Bulwark of the Primordial Mound (Halls of Origination, Earthrager Ptah)
84 – Truthbreaker Shield (Quest, A Villain Unmasked (alliance)), Twilight Mirrorshield (Quest, Traitor´s Bait (horde))
85 – Elementium Earthguard (AH, Crafted), Extinct Turtle Shield (Archaeology), Shield of Four Grey Towers (JP Vendor), Blockade's Lost Shield (AH, BoE (epic))
Removed or changed shields in Cataclysm
18 - Arctic Buckler (Quest, Blackfathom Villainy) REMOVED
23 - Marbled Buckler (Quest, A vengeful fate (horde), The Crone of the Kraul (alliance)) REMOVED
27 - Heart of Agamaggan (RFK, Charlga Razorflank) CHANGED
30 - Vigilant Buckler (Quest, Malin's request (alliance only)) REMOVED
32 - Pit Fighter's Shield (Quest, Trol'kalar (horde only)) REMOVED
55 - Argent Defender (Quest, The Argent Hold) REMOVED
57 - Dreadguard's Protector (DM West, Lord Hel'Nurath) REMOVED?
If you notice anything incorrect, please tell me :)
Thanks to Wowhead.com for helping me do this list!