Many players have chimed in so far with their fondly remembered misadventures. Tirion Fordring's Redemption chain out of the Eastern Plaguelands gets many recommendations. As does the Marauders of Darrowshire chain in which you have to find a little girl ghost's missing dolly and along the way relive a critical moment in the history of the lands.
You can also summon a helicopter out of Azshara, get killed on purpose out of Un'goro and learn the history of the Moonkin which takes you to the same area where you can quest for a mechanical yeti. But there is one quest that is getting the most enthusiastic recommendations.