Ankha

Ankha is a rare spawn with approximately 232k health (added in patch 4.2) and is located in Mount Hyjal in The Regrowth. I have highlighted the area she patrols in purple on the map below. Ankha shares a spawn timer with Magria who is a very similar looking spirit beast. Their spawn timer is somewhere between 6 and 17 hours. The NPCScan id for her is 54318, you will need to add it to NPCScan in order for it to find her. You also need to have completed enough quests in Mount Hyjal to have unlocked the daily quests at The Sanctuary of Malorne to be able to see Ankha and Magria. The final quest before unlocking the dailies is Aessina's Miracle.

Ghostcrawler

Ghostcrawler is a level 85 rare spawn with approximately 1.5 Million health located in the Abyssal Depths in Vash'jir south of L'ghorek. He is a neutral mob and he has a very large patrol area as you can see from the map below in blue.

Ghostcrawler is a tribute to Greg Street aka "Ghostcrawler," the Lead Systems Designer for World of Warcraft. The mob's Nerfbat ability (which has the tool-tip "an unfair attack that reduces all skills." and debuff which "Nerfs all skills "To the ground!"") is also a tribute to him. During an interview a couple of years back Greg was asked if Ret paladins would be nerfed and his response was "TO THE GROUND BABY."

Vyragosa

Vyragosa is a level 80 rare dragon found in the Storm Peaks in Northrend. Vyragosa has four separate flight paths which are shared with the Time-Lost Proto Drake. The flight paths Vyragosa can take are shown in four separate colors on the map below along with her spawn locations. Vyragosa has 18,900 hp. This npc is part of the Northern Exposure and Frostbitten achievements. Vyragosa drops Azure Dragonleather Helm which is a level 78 bind on equip helm with a random enchantment. Like other Northrend rares, Vyragosa also drops Abandoned Adventurer's Satchel, which generally contains about 20 gold, a full stack of frostweave cloth, and often times a few crystallized elements. 

Most people usually find Vyragosa while looking for the Time-Lost Proto Drake because they share a spawn timer and flight paths meaning that the two can never be up at the same time. Vyragosa is also much more likely spawn than the Time-Lost Proto Drake. 

Skoll

Skoll is a level 80 non-hostile rare mob with 18,900 health. He can be found in the Storm Peaks in several different locations which are indicated in blue below. This npc is not part of any achievements (most likely because he is a tamable hunter pet). He drops Skoll's Fang which is a level 78 bind on equip main hand dagger item with a random enchant. Like other Northrend rares, he also drops Abandoned Adventurer's Satchel, which generally contains about 20 gold, a full stack of frostweave cloth, and often times a few crystallized elements.

Skoll is a tamable hunter pet. Please note that because he is a hunter pet that even though you may not have seen Skoll before in Storm Peaks it doesn't mean that he isn't already cached by NPCScan. If a hunter has this tamed pet out near you, your NPCScan will cache it. If it is cached in NPCScan and this rare is up your alert will not go off. Be sure to check and clear your cache often!

Captain Florence

Captain Florence is a level 81 non-elite rare spawn located on a ship floating in the water above the Shimmering Expanse just south of Nespirah. He is only hostile toward Horde players. Alliance's version of this NPC is Captain Foulwind who spawns in the Horde ship north west of Captain Florence. He is not a flagged npc, so killing him will not flag you on a non-pvp server. Captain Florence doesn't drop anything of value, not even a decent amount of gold. He generally drops around 2g, and sometimes embersilk cloth or grey items. He does offer a very decent amount of experience though for players leveling in the area; approximately 42k xp non-rested at level 82. If your level 85 and you come across this guy, don't bother killing him, you really have nothing to gain.

Dirkee

Dirkee is a level 80 rare elite found in a few different locations in the Storm Peaks in Northrend. The locations he can spawn at are shown in green below. He has approximately 50k hp and he hits pretty hard so don't take him too lightly. This npc is part of the Northern Exposure and Frostbitten achievements. He most often drops Titanium Brain-Gear which is a level 76 bind on equip ring with a random enchantment. About 10% of the time he will drop Dirkee's Superstructure which is a level 80 bind on equip 2 handed mace . Like other Northrend rares, he also drops Abandoned Adventurer's Satchel, which generally contains about 20 gold, a full stack of frostweave cloth, and often times a few crystallized elements.

Dirkee hits pretty hard. If you are above level 80 he shouldn't be too tough, but those leveling in the area that come across him should take some extra precautions. He does a kick called Mechano Kick which has a 40 yard range as well as an ability called Suppressive Fire which deals fire damage. Dirkee's corpse can also be salvaged by engineers.