Rawr is the offical companion addon to Rawr (http://rawr.codeplex.com).
Rawr is a web based program that allows you to view your character out of the game and to try out different gear to see how that affects your tanking/dps/healing. It includes an optimiser so you can tell it what gear/gems/enchants you have available and it will workout for you what the best setup of gems/enchant/reforging etc is based on what you have available. It takes into account things all sorts of things like hit caps, special trinket procs etc, to make sure your character is geared the best it can be with the gear you have available.
This in game addon allows users to export their character details directly into Rawr in one simple operation. No more having to log out and wait for armoury updates, no more wanting lists of stuff in your bags/bank to be included and relying on out of date addons that are no longer supported.
Once you have adjusted the gear on your character in Rawr or optimised it you can then use the export to addon feature in Rawr to pull the data back in game to see how everything looks. It also maintains an upgrade list in game so you have a reference to what items to look out for. It can also play a sound in game and warn you when an item in your upgrade list drops from a mob or is linked in raid/party chat.
Rawr 4.0.15 and above supports Rawr.Addon it can be found at http://elitistjerks.com/rawr.php
Please rate this addon on Curse.com, and add it to your favourites to ensure you get the latest updates.
Future features: I plan to add features like visual/sound alerts when an item drops that is in your upgrade list. So you can easily tell that the thing that has just dropped is an upgrade for you. I'm also keen for users to suggest new features please use the ticket system http://wow.curseforge.com/addons/rawr-official/tickets/ to make your suggestions.