But the main rare monster you should note is Poseidus, which will drop an epic underwater mount (Reins of Poseidus) that binds when used! That means you can sell it to other players. Expect to get even 30,000 gold for it, assuming Poseidus stays as rare as it is currently. He can be soloed easily, as he's only level 81 non-elite.
The day before the patch goes live, you should park your toon where Poseidus spawns and start camping it right away once it goes live! To see it's spawn points, click on the name!
Other rare elites that will drop BOE epics:
Do note that 4.1 is still in PTR and it's highly likely that the reins will become BOP before 4.1 hits live realms!
★ Check the Elite Gold Making page for the best gold making tricks ★
★ Use the automated gold making addon and make 30,000 gold a day ★
★ Read the Most Secret Gold Making Tricks that even I cannot mention! ★
★ Level alts & professions. 1-90 in 2½ days is the record with this addon ★