Topic Addon to tell rarity BEFORE battle?
You'll have to actually start the battle before even Quality Notifier will let you know.
What I do is have an overpowered (for the rare I'm hunting) pet first in the lineup and the others appropriate level. That way if it's not a rare (or there's a rare a few pets in) they can just smoosh the non-rares, then you can rotate in your lower-leveled pets to wear the rare down for capture.
Edited by Buffinlovin on 10/10/12 4:31 PM (PDT)
Here are the add-ons I use to help me with my goal of having all the wild caught pets as rares:
Battle Pet-Quality Notifier. What this one does is allows me to hover my mouse over the little minimap paw and it will tell me if I own it, and the name will be grey/white/green/blue depending on the highest quality of the pet that I own. This allows me to fly over all those Mouse and Rabbit pets much easier knowing I already have rare versions of them haha!
Battle Pet-Count. I will catch multiples of rares if I think their stats or level are different. This tells me when I hover my mouse over the pet in game BEFORE I battle or if I hover over their nameplate DURING battle how many of that pet I own, and what level they are.
PetBattle Teams-This allows me to put together quick teams to choose from without manually having to drag them to the interface. The UI on this is a bit clunky to start, but once you get the hang of creating the teams its really really great t ohave.
Pokemon Trainer-the Pet Battle Mod. I cannot live without this addon! Once you are active in combat, there are two panes that open up on the left and right hand sides of the screen. The panes on the left side will display your pets' abilities, and the pane on the right will display the opposing pets abilities, and you can determine what spells to use based off if it does good damage, average damage, or weak damage. A better explanation of this addon (and I think a couple others here too) can be found here http://wow.joystiq.com/2012/10/04/addon-spotlight-still-more-pet-battle-addons/
As far as what you're looking for, where it tells the rarity before battling, I do not think that will ever happen. People will then just hunt the rare spawns and leave the rest, and I don't think that's Blizzard's intention. The addons I use are just to help me make battling more efficient so I'm not wasting so much time using weak spells or trapping pets that are not the quality I need.
Edit: Whoa bad spelling haha!!