Blizzard recently added a new section to the official WoW armory, a "Companions & Mounts" area. You can access it through your character's armory page. It's located on the left navigation bar, just below your character's "Achievements" link.
In the new "Companions & Mounts" section, you can view all the vanity pets that particular character owns and the pets that have yet to collect. Unfortunately, you cannot view companions that are no longer available or regional pets that may be unobtainable.
There's an advanced filter option that has the standard selection of choices to help you sort through your collection. It may not be as detailed as the filters available on WarcraftPets or include an option to sort by pet type, but it beats browsing and searching through all the companions one by one and page by page!
While this new collecting section of the official armory may not be as detailed or in depth as WarcraftPets, it will still come in handy for double checking collections and if our favorite fansite ever goes down for maintenance the armory will be there as back up.
Interfacing with WarcraftPets
Additionally, we're currently working on changes to WarcraftPets so that user accounts will interface with the pet data found in a character's official armory profile. When these changes roll out in the months ahead, collections will be validated against the armory and updating your collection will be a breeze.
Official Armory Collection Tracking
July 11, 2011