WoWhead introduced a pretty amazing new feature based on some new API goodies in 4.0.3. Specifically, they introduced what they're referring to as Personalized Search.
You'll need to run the WoWhead client addon, and then upload your data to them after a session, but once you've done so, you'll be able to search and filter quests, mounts, recipes, achievements, pets, titles and more based on what you've completed, and what you haven't. Just log in to WoWhead, and set a default character, and it will automatically filter by any informaiton needed.
The real power of this comes when you view a list of quests for a zone, then you filter for ones that are 'available' and for your faction. This will give you a list of quests you can accept immediately, and hopefully will get you well on your way to Realm First once Cataclysm launches. Don't forget, though, this works for all data types that show up in the Profiler, including mounts, companions, recipes, quests, achievements, titles, and actions.