Everybody has given good info, so my only additions:
*corrupted shaman in Lake Rathetear, loot Clean Lakewater
The waiting is the hardest part and goblins are incredibly annoying underwater. Harmony everything in the tower and pull the PH/tainted away, preferably so your backs against a wall. Be ready to spend ~12-24 hours camping him.
*Corrupted Seahorse in Kedge Keep, loot Kedge Cave Crystals
This is the only spirit I'd tell someone to buy a MQ for, as Kedge is a huge PITA and it's a big ask to get help for potentially 4-5 hours to spawn him. You can find the MQ for ~4k fairly often, or find a few friends for the hunt. I hear the hardest part is getting tainted to spawn.
*Corrupted seafury cyclops in Ocean of Tears, loot Ocean of Tears Seavines
Tainted is almost always up, ask a Necro sitting in line at AC for help. Trivial to fear kite at 55+, which you'll want to do as he summons.
*Corrupted brownie in Lesser Faydark, loot Green Heartwood Branch
The PH for tainted spawns at 0,0 and proceeds to wander. If you go northwest a little from 0,0 to the road nearby and wait, you will find him pathing. After you clear, sit at 0,0 and wait ~7mins for respawn. Summons and is trivial for a 55+ necro to solo.
*Ulump Pujluk in Swamp of No Hope, loot Froglok Essence
Enchanters can solo this, but its easier/less stressful to find a tank+cleric+enchanter to help you. Ranger/SK/Pal/War and I bet even a Bard can tank him. Runs at 20%. Use
Grik for your Ench's pet.
*Corrupted Gorilla in Emerald Jungle, loot the Green Tree Bark
Go to the north-west area of EJ, on top of the plateau. Round up gorillas (both undead and alive) and quad them down. Keep clearing them until tainted pops, then pull it back towards FoB to root rot. Some people have bad luck getting him to spawn, but killing every gorilla I found it only took me ~1-2 hours to get a tainted.
*Corrupted barracuda in Lake of Ill Omen, loot the Pure Lakewater
There is a 30 second respawn for the barracuda near the dome, which you'll want as the corrupted is a very low % pop on tainted's death. Just kill PHs and tainted with ESVs. Repops will assist the corrupted.
*Faydedar in Timorous Deep, loot the Pod of Seawater
The spawned version is slowable and only takes one group. 60 Tank+Cleric+Dps+Ench/Sham+You can kill him. I imagine some of the better geared players could duo/trio.