On this past St. Patrick's Day, guild members were doing the quest chain in Hellfire that rewards you Mirren's Drinking Hat. At the time my main was doing this chain, I wasn't the connoisseur of hats that I am now. 10 and counting. Yet another reason for Blizzard to make wardrobes (urge to rant rising.) Several guild members have that hat and it provides much laughter when they pull a random brew from it. I, however, am so sorry I didn't save it. 2 gold for selling it was, at the time, a lot of money for a perpetually broke dwarf and I had a "better" hat for questing.
Yes, I know. A dwarf tossing away a drinking hat! That alone is almost sacrilegious. But sold it I did. Now, when guild members pull some brew out of their hats, I regret my decision and I'd go do the quest chain again in a heartbeat just to get that hat. I'd have to toss something from my inventory (Archmage Vargoth's Staff maybe, or Monster Slayer's Kit, neither of which I use but are awesome in their own right) to carry it around in my bags, but I'd do it to get that hat.
How about you? Is there any quest reward that you sold or otherwise disposed of that you'd do the quest chain to get again?