8. Shattered Sun
The last of the factions added to the game in BC, you can get exalted with the Shattered Sun by running normal or heroic Magisters' Terrace and/or doing the Shattered Sun dailies on the Isle of Quel'danas. Because Kael coughs up a pet (and a mount on heroic) and all of the heroic bosses have a chance of dropping the Orb of the Sin'dorei, I'd advise the former if you can swing it, although as we noted in the previous OverAchiever, soloing him even at 80 can be risky.
Shattered Sun quartermaster: Eldara Dawnrunner at 47,30 on the Isle of Quel'danas.
9. Aldor or Scryers
You'll have to pick one or the other here, as this reputation grind is zero-sum; every gain you make for the Aldor will result in a reputation loss with the Scryers and vice versa. Getting exalted with both of them (although obviously not at the same time) will give you the Feat of Strength Hero of Shattrath, though. Get exalted by exhausting either faction's quest offerings (Aldor or Scryer) then doing one of the following:
If you're an Aldor: turn in Marks of Sargeras for 250 rep to Adyen the Lightwarden at 30,34 on the Aldor tier in Shattrath, and Fel Armaments for 350 rep to Ishanah at 24,25 on the Aldor tier. Both of these are BoE, so keep checking the AH.
If you're a Scryer: turn in Sunfury Signets for 250 rep to Magistrix Fyalenn at 45,82 on the Scryer tier in Shattrath, and Arcane Tomes for 350 rep to Voren'thal the Seer at 42,91 on the Scryer tier. These are also BoE, so the same rule concerning the AH applies.
Aldor quartermaster: Quartermaster Endarin at 48,26 in the Aldor bank in Shattrath.
Scryer quartermaster: Quartermaster Enuril at 60,64 in the Scryer bank in Shattrath.
I really adore this faction, particularly after Blizzard added the little sporeling pet at exalted, but I dearly wish their sense of tabard design were somewhat better. Get exalted by exhausting quest offerings and doing the repeatable kill quest, turning in Sanguine Hibiscus (in batches of 5) from Underbog, and/or turning in Fertile Spores from creatures in Zangarmarsh. Each is repeatable and will reward 750 rep a pop. Fair warning; before purchasing one of these tabards (either from their quartermaster or a tabard vendor elsewhere) you will need 10 Glowcaps, which can only be picked in Zangarmarsh (particularly western Zangarmarsh). Fortunately they're all over the place, so it shouldn't take you long to get 10.
Sporeggar quartermaster: Mycah at 18,51 in Sporeggar (western Zangarmarsh).
Get exalted by exhausting their initial quest offerings, starting with Speak with the Ogre (the quest chain to unlock Ogri'la quests and dailies doesn't award any rep, but a few non-daily quests immediately afterwards do) then doing dailies. Most, if not all, of the initial questline should be easily soloable for most classes at 80, particularly since Blizzard changed one the last quests so as not to require a full group of 5 people. As with Sporeggar, purchasing a tabard from the ogres isn't as simple as forking over some cash; you'll need 10 Apexis Shards in hand to buy a tabard from either the Ogri'la quartermaster or a tabard vendor elsewhere.
Ogri'la quartermaster: Jho'nass at 27,59 in Ogri'la (western Blade's Edge, accessible only with flying mount).
You'll get some spill-over Sha'tar rep from doing turn-ins for the Aldor or Scryer up until Honored, and after that you should pretty much bank on running the three Tempest Keep 5-mans (Botanica, Arcatraz, and everybody's favorite, the Mechanar) on either normal or heroic afterwards. If you're working on Scryer rep, the TK instances should also drop their rep items.
Sha'tar quartermaster: Almaador at 51,42 in central Shattrath.
I have yet to find an armor set that looks good with the Skyguard tabard, but to each his own. Once you have Expert riding (as with Ogri'la, you'll need a flying mount for this), speak to Yuula (next to the flight master in Shattrath at 63,42) to get started with Threat From Above, the questline that will grant you eligibility to do Skyguard dailies. After that, it's dailies, dailies, dailies, although you'll unlock the ability to complete some Skyguard dailies in Ogri'la as well, with a convenient (and free!) flight path in between at Honored. You can also speed the process up somewhat by doing the Terokk chain, although (as with farming heroic instances at 80) you may or may not be able to solo this.
Skyguard quartermaster: Grella at 64,63 in the Skyguard camp in eastern Terokkar Forest.
Righty-o. We're a little more than halfway to our goal of 25 tabards, so let's keep moving:
Wrath of the Lich King faction tabards
Getting Wrath faction tabards is significantly easier, as you only have to be friendly with factions in order to acquire them, and that's pretty much a doddle if you so much as sneeze in the direction of your average Wrath questline:
14. Tabard of the Ebon Blade
You have to quest for a bit in Icecrown in order to access the Ebon Blade quartermaster, so this tabard won't be immediately available upon arrival in Northrend. Get started on the chain that begins with It's All Fun and Games, and this is all easily soloable.
Ebon Blade quartermaster: Duchess Mynx at 43,20 in the Shadow Vault (northern Icecrown) after you phase this hub into existence.
15. Tabard of the Kirin Tor
As with Skyguard, I have yet to find a way to make this tabard look good with an armor set, but at least it's easy to get. Doing the basic set of Kirin Tor quests out in Borean Tundra and around the Nexus will get you well into Friendly (if not Honored), and after that you can simply drop into Dalaran and pick up your very own horribly garish tabard, resplendent in all its eye-blinding glory.
Kirin Tor quartermaster: Archmage Alvareaux at 25,48 in the Violet Citadel in Dalaran.
16. Tabard of the Argent Crusade
Questing through Gun'drak should put you comfortably into Honored with the Crusade. If not, you'll have plenty of opportunities to get rep in Icecrown.
Argent Crusade quartermaster: Veteran Crusader Aliocha Segard at 87,75 in the Argent Vanguard, extreme southeastern end of Icecrown (under the tent on the hill where Tirion Fordring is initially located).
17. Tabard of the Wyrmrest Accord
Dragonblight quests are the way to go to reach Friendly, although if you don't have Cold Weather Flying, be prepared to spend a lot of time going up and down on taxi-dragons to get between the bottom and top of the Temple. I'm sure a machinima version of Vertigo could easily be shot here.
Wyrmrest Accord quartermaster: Cielstrasza at 60,53 (the top of the Wyrmrest Temple in Dragonblight).
The ease of getting these will depend on how quickly (or not) you can amass tokens from battleground play and how much time you spend in arenas and BG's. For people who PvP a lot, you may already be sitting on a lot of the tokens, wins, or reputation you need; if you don't, some of it's probably too time-intensive to count on getting quickly. The frustration factor will also mount quickly if you don't have a lot of resilience and can realistically expect to be gunned down quickly in battlegrounds, so it might be worth your time to invest in a set of PvP gear if you're depending on PvP tabards to get you to 25.
In the (rough) order of the easiest to the hardest:
18. Private's Tabard (Alliance) or Scout's Tabard (Horde)
Available for 3 Warsong Gulch marks and 3 Arathi Basin marks from Master Sergeant Biggins for Alliance (75,63 in Stormwind) or Brave Stonehide for Horde (38,64 in Orgrimmar). Even if your faction has displayed a marked talent at losing these battlegrounds, 6 tokens aren't too hard to get.
19. Knight's Colors (Alliance) or Stone Guard's Herald (Horde)
Somewhat more time-consuming, these tabards can be bought with 20 Warsong Gulch marks, 20 Arathi Basin marks, and 20 Alterac Valley marks from the same NPC's listed above. If your faction doesn't habitually win these BG's, I won't lie -- it's going to be a grind.