Medium Rare

Rares by zone:

• Hellfire Pennisula
  
  • Fulgorge - 62 Rare Chest Burster. Can spawn in any location with regular Chest Bursters.
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  • Mekthorg the Wild - 61 Rare Orc. Spawns in any Orc Camp (Zethgor or along the Longitude of of Hellfire Citadel).
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  • Vorakem Doomspeaker <Herald of Doom Lord Kazzak> - 62 Rare Demon. Spawns amongst other Demons (Legion Front, Forge Camps, and Pools of Aggonar).
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• Zangarmarsh
  
  • Marticar - 63 Rare Fen Strider. Patrols the West Coast out past Sporeggar, the Northern Edge above Coilfang, or the NE edge just outside the Dead Mire.
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  • Bog Lurker - 63 Rare Bog Giant. Spawns amongst the broken one tribes. S of Cenarion Refuge, S of the Twin Spires, or West of Orebor.
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  • Coilfang Emmisary - 63 Rare Naga. Spawns amongst the 4 Naga camps in Zangarmarsh.
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• Terokkar
  
  • Crippler - 65 Rare Skeleton. Spawns in and around the undead of Auchindoun proper in the Bone Wastes.
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  • Doomslayer Jurim - 64 Rare Draenei. Patrols the roads South and West of Shattrath (as far as the road into Shadowmoon Valley), though he can cross paths with and be killed by patrolling Shattrath Guards.
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  • Okrek - 64 Rare Arakkoa. Spawns in any of the 4 Arakkoa camps throughout Terokkar (exludes the camp SW of the Bone Wastes, apparently)
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• Nagrand
  
  • Goretooth - 65 Rare Crocolisk. Any of the major lakes of Nagrand (Aka, SE of the Zone, S of Throne of Elements, Around Nagrand, or by Sunspring Village)
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  • Voidhunter Yar - 68 Rare Void Monstosity. Spawns around Oshu'gun.
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• Blade's Edge Mountains
  
  • Morcrush - 68 Rare Crystal Giant. Spawns in the area surrounding, and North of, Death's Door.
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  • Hemathion - 68 Rare Dragon. Spawns out in the Western Edge of the zone.
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  • Speaker Mar'grom - 68 Rare OgreMagi. Spawns within Ogre camps.
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• Netherstorm
  
  • Nuramoc - 70 Rare Chimera. Can spawn Southern Edge of Area 52's Island, Northern Ridge above Manaforge Duro, or the Western Ridge of the Stormspire Island.
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  • Ever-Core the Punisher - 68 Rare Arcane Construct. Patrols any of the Mana Forges B'naar, Ultris, or Ara.
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  • Chief Engineer Lorthander - 69 Rare Blood Elf. Patrols Mana Forges Ara, B'naar, and Coruu.
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• Shadowmoon
  
  • Collidus the Warp-Watcher - 68 Rare Beholder. Patrols the SE world edge, NE world edge, or just South of the the Deathforge.
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  • Kraator - 68 Rare Infernal. Legion Hold's Foothills, Eclipsion Fields, North of Coilskar, or North of the Warden's Cage.
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  • Ambassador Jerrikar <Servant of Illidan - 69 Rare Satyr. Spawns in any of the areas under Illidan's control (Illidari Point, Eclipsion Point, Coilskar Point, N of the Warden Cage, or the Orc camp S of the Black Temple)
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Note that this one has been excluded from the Achievement, probably due to error.
Bro'Gaz the Clanless - 66 Rare Ogre(?). Spawns along the North-South road in Western Nagrand, the roads just north of Telaar, or SW of Telaar near Kil'Sorrow Fortress.

All-in-one targeting macro (255 chars):

/tar Fulgor
/tar Mekt
/tar Vorak
/tar Martic
/tar Bog Lurk
/tar Coilfang Em
/tar Crip
/tar Doomsay
/tar Okrek
/tar Goretoo
/tar Voidhunt
/tar Morc
/tar Hema
/tar Speak
/tar Nura
/tar Ever-Core
/tar Chief Engineer L
/tar Collid
/tar Kraat
/tar Ambassador J

As you're flying around Outland, just spam this until it hits. Please leave a comment if there are any false positives.

Edit (2008-10-18): Just found Marticar at (40,33) using this macro. Flew through all of terokkar, smv, hellfire, then zangar -- no false positives in any of those zones. Good luck hunting!

Edit (2008-10-19): Rearranged a bit to eliminate Area 52 false positive -- thanks GIDustin! Also corrected an error -- "Coilfang Emm" would never target the intended mob; replace with "Coilfang Em".

Edit (2009-03-16): Just finished Bloody Rare, using my above macro the entire time. Everything targets except Fulgorge (unless it's a Fulgorge corpse /cry). Good luck hunting!

Download the addon Super Duper Macro and use this:

/cleartarget
/tar Ambassador Jerrikar
/tar Chief Engineer Lorthander
/tar Collidus the Warp-Watcher
/tar Doomsayer Jurim
/tar Fulgorge
/tar Hemathion
/tar Marticar
/tar Morcrush
/tar Okrek
/tar Voidhunter Yar
/tar Bog Lurker
/tar Coilfang Emissary
/tar Crippler
/tar Ever-Core the Punisher
/tar Goretooth
/tar Kraator
/tar Mekthorg the Wild
/tar Nuramoc
/tar Speaker Mar'grom
/tar Vorakem Doomspeaker
/stopmacro [noexists]
/tell YOUR NAME HERE > %t <
/stopmacro [dead]
/run
/run RaidNotice_AddMessage(RaidBossEmoteFrame,"THERE IT IS! KILL IT!", ChatTypeInfo["RAID_WARNING"])
/run RaidNotice_AddMessage(RaidBossEmoteFrame,"THERE IT IS! KILL IT!", ChatTypeInfo["RAID_WARNING"])
/run RaidNotice_AddMessage(RaidBossEmoteFrame,"THERE IT IS! KILL IT!", ChatTypeInfo["RAID_WARNING"])
/script PlaySoundFile("Sound\\interface\\RaidWarning.wav")

If you use that you can't miss if you get target of one of them.

Enjoy!