Northern Exposure and Frostbitten Achievement Guide

If you're only doing Northern Exposure, you only need one of these. I've categorized them by area so you can find the one in the area you're questing. Once you've done Northern Exposure, you'll unlock Frostbitten, which requires all of these kills. Whichever one you're doing, here's the list:

Howling Fjords:

Vigdis the War Maiden

Scholozar Basin:

Loque'nahak

Aotona

King Krush

Icecrown:

High Thane Jorfus

Hildana Deathstealer

Borean Tundra

Old Crystalbark (Coldarra)

Fumblub 

Storm Peaks:

Dirkee

Vyragosa

Dragonblight:

Crazed indu'le Survivor

Tukemuth

Zul'drak:

Zul'drak Sentinel

Terror Spinner