To All The Squirrels Who Shared My Life

Here's the locations, sorted so you can pick them up in a big clockwise circle around Northrend

Eastern Kingdoms

Huge Toad - Swamp of Sorrows http://www.wowhead.com/?npc=6653
Lava Crab - Searing Gorge http://www.wowhead.com/?npc=9700

Northrend

Arctic Hare - Dragonblight, Borean Tundra, Zul'Drak http://www.wowhead.com/?npc=29328

Tundra Penguin - Borean Tundra http://www.wowhead.com/?npc=28440
Borean Marmot - Borean Tundra http://www.wowhead.com/?npc=31685

Sholazar Tickbird - Sholazar Basin http://www.wowhead.com/?npc=28093

Glacier Penguin - Icecrown http://www.wowhead.com/?npc=32498

Grizzly Squirrel - Grizzly Hills http://www.wowhead.com/?npc=31889
Mountain Skunk - Grizzly Hills http://www.wowhead.com/?npc=31890 (after you get Grizzly Squirrel, remove Grizzly Squirrel from the macro so it will select Mountain Skunk)

Scalawag Frog - Howling Fjord http://www.wowhead.com/?npc=26503
Fjord Penguin - Howling Fjord http://www.wowhead.com/?npc=28407
Fjord Turkey - Howling Fjord http://www.wowhead.com/?npc=24746

Use the following macro to /love these critters:
/tar Arctic Hare
/tar Fjord Penguin
/tar Glacier Penguin
/tar Huge Toad
/tar Mountain Skunk
/tar Sholazar Tickbird
/tar Borean Marmot
/tar Fjord Turkey
/tar Grizzly Squirrel
/tar Lava Crab
/tar Scalawag Frog
/tar Tundra Penguin
/stopmacro [noexists]
/love

This is where I personally found all of them for this achievement by zone:

~~BOREAN TUNDRA~~
Borean Marmot 51, 73
Tundra Penguin 62, 68

~~HOWLING FJORD~~
Fjord Penguin 19, 56
Fjord Turkey 68, 65
Scalawag Frog 36, 79

~~DRAGONBLIGHT~~
Arctic Hare 28, 50

~~GRIZZLY HILLS~~
Mountain Skunk 57, 35
Grizzly Squirrel 43, 48

~~SHOLAZAR BASIN~~
Sholazar Tickbird 27, 60

~~ICECROWN~~
Glacier Penguin 67, 25

~~SWAMP OF SORROWS~~
Huge Toad 14, 60

~~SEARING GORGE~~
Lava Crab 42, 37

EDIT: I'm not quite sure why this is being rated down, this is a complete guide by zone for this achievement and all coords confirmed when I did it.

If you want to do [To All The Squirrels Who Shared My Life] and [Pest Control] together, both and in some sort of order:

Northrend:
Kill: Devouring Maggot - Howling Fjord 57,55 in the Utgarde Catacombs on the bottom pit with all the ghouls
/love: Fjord Turkey - Howling Fjord 67,67
/love: Fjord Penguin - Howling Fjord coasts around 21,61 and 66,83
/love: Scalawag Frog - Howling Fjord 36,80
Kill: Fjord Rat - Howling Fjord
Kill: Roach - Howling Fjord 36,11 and several other places / instances
/love: Mountain Skunk - Grizzly Hills
/love: Grizzly Squirrel - Grizzly Hills
Kill: Zul'Drak Rat - Zul'Drak 45,63 around the Amphitheater
/love: Arctic Hare - Zul'Drak 56,78 e.g., Dragonblight, Borean Tundra
Kill: Gold Beetle - Halls of Lightning just behind entrance, Halls of Stone
/love: Glacier Penguin Icecrown 69,20
/love: Sholazar Tickbird - Sholazar Basin 27,60
/love: Borean Marmot - Borean Tundra
/love: Tundra Penguin - Borean Tundra at several coast spots
Kill: Crystal Spider - Nexus around Keristrasza, Oculus
Kill: Underbelly Rat - Dalaran Sewers

Naxxramas: (Gotta go there anyway, assuming you don't want to travel to Ghostlands)
Kill: Larva - Naxxramas Plague Wing, Ghostlands
Kill: Rat - Naxxramas, Arathi Basin (Farm if Horde controlled) and a lot of other places
Kill: Spider - Naxxramas entrance, several LK 5 man instances and several other places
Kill: Maggot - Ghostlands, Naxxramas entrance, Underbog

Outland:
Kill: Adder - Hellfire Peninsula, Nagrand, Durotar, Barrens
Kill: Scorpion - Hellfire Peninsula, AQ20, AQ40

Eastern Kingdoms:
Kill: Mouse - Westfall
Kill: Snake - Westfall and several other places / instances
Kill: Moccasin - Swamp of Sorrows
/love: Huge Toad - Swamp of Sorrows
Kill: Fire Beetle - Searing Gorge, Burning Steppes, Shattered Halls
/love: Lava Crab - Searing Gorge, Burning Steppes