Acid Elemental [Renowned], Fire Daemon [Renowned], Fire Elemental [Renowned] and Goblin Alchemist & Mage [Renowned] are all pretty easy especially for an archer with a slayer bow.
Ratman chieftains (Vitavi [Renowned], Rakktavi [Renowned], Tikitavi [Renowned]) have too much hitpoints (guess about ~50,000) so while they are good for training or to get a re-spawn, they are boring to fight. Especially, before the publish 65, their loot was somewhat similar to a regular ratman loot so most people thought they dont worth the effort.
Pixie [Renowned] and Wywern [Renowned] are tougher than the above. Wyvern [Renowned] is very similar to an Ancient Wyrm (only with a little more hitpoints) and Pixie [Renowned] is again great for pet training but it needs a Fey slayer weapon and takes time to kill (about ~9,000 hitpoints).
I havent yet to face Devourer of Souls [Renowned], Ancient Lich [Renowned] or Skeletal Dragon [Renowned], so If anybody has any information regarding them, it will be very useful.