This question is actually a tough one for me to answer. Not because I don't have an answer but because I have entirely too many answers. My bags and bank are stuffed full of random items that I refuse to get rid of, even now-useless stuff like Shard of the Fallen Star. I guess if I had to choose, I'd say it'd be a tie for two: my Orb of Deception and Orb of the Sin'dorei. I love turning my night elf into an undead or blood elf, respectively, though unfortunately the Orb of Deception requires being equipped in a trinket slot to work, so it's not very practical for raiding. The Orb of the Sin'dorei you can just click to use. True story: once upon a time back in Wrath I was hanging out, transformed into a blood elf, at the Ulduar summoning stone helping bring my guildmates to the raid. Another Alliance player walked up and /spit on me. When I whispered him with a frowny face emote, he freaked out and thought I was a hacker. Helpful tip, my friend: a blood elf in full tier 7 druid gear is not actually a blood elf! Also, you shouldn't /spit on people, it's really rude!