There is a nice guide to the pre-cata versions of this achivement. However, "the cataclysm brought new critters to Azeroth, show them you love them" or something similar. Here is where to find them all.
I have tried to put them in a decent order to speed finding of them up.
Obviously, fly between them with the nice new Cataclysm flying as most of these require Cataclysm to find. Some don't, so go find now!
Eastern Kingdoms
Yellow-Bellied Marmot - Twilight Highlands
Highlands Turkey -Twighlight Highlands
Baradin Fox Kit - Tol Barad
Sassy Cat - Tol Barad
Sea Cucumber - Shimmering Expanse (Vashjir)
Rockchewer Whelk - Shimmering Expanse (Vashjir)
Wharf Rat - Booty Bay
Kalimdor
Alpine Chipmunk - Winterspring
Grotto Vole - Mount Hyjal
Rock Viper Desolace
Oasis Moth - Uldum
Mac Frog - Uldum
Rattlesnake - Tanaris
Thankyou for looking/reading.