In general, any item that can be turned in repeatedly for reputation will be valuable for someone. Reputation with certain factions can help you buy a mount other than the one that comes standard for your race. Some people would rather do that, or gain faction to get a discount on their mount. Also, faction reputation gains access to interesting items and plans for various professions. Some faction items that I have found valuable and easily sellable for good gold: Morrowgrain, Incendosaur Scales, Stacks of Cloth (especially Runecloth), Twilight Texts (Silithus), Bijous or (Zul’Gurub), Leather, Kingsblood (for Thorium Brotherhood). In general the pre-BC items aren’t as valuable, but the lessons learned in the past still apply.

Now the hot items have to do with Aldor or Scryer rep (Arcane Tome, Fel Armament, Marks of Sargeras, Sunfury Signets), or something like Coilfang Armaments and Sanguine Hibiscus. Any time you discover an item that’s being used for faction rep gain, if you’re not interested in that faction, just remember that other people might be, and might be willing to pay dearly for it. For a complete list of Factions and the items used for their rep gain, go to the Reputation page on WoWWiki.com.