With the release of The Shattering, the complete revamp of quests from levels 1-60 and the introduction of new sub-achievements for Loremaster of Eastern Kingdom and Kalimdor, a lot of people have been revisiting these old zones. However, some, but not all by any means, don't really have an idea of the location of most quests, what mobs drop items that begin quests etc.
I came across an add-on called QuestHubber. It is designed to show pinpoints on the world map of all the quests you've missed; for a zone you haven't visited, this means all quests. Between data personally collected by the author, data submitted from other users, and data obtained from Wowhead, there are over 4,000 quests for Alliance and Horde from every zone and continent in game currently—including the new Cataclysm zones.
QuestHubber has been fine tuned since it first came out the day after 4.0.3a. However further help is always welcome.
QuestGather, an optional bundled addon, is used to gather data of NPC and quest locations as you are questing. You may disable or delete this if you do not wish to collect data.
If you want to contribute the information you've gathered, please locate the following file:
World of Warcraft\WTF\Account\(account name)\SavedVariables\QuestGather.lua
Zip and email this to addons@nca-guild.com.
I use Tekkub's TourGuide, which is awesome, but it's not updated to the new stuff. Might see if I can run them in tandem to support the crowd-source gathering efforts.