By the raids that appear often you can find bosses like:
ZAO:
- Grand Mother Foulscale - it spawn 25 minutes after announced raid
- The Blightfather - it spawn after 30 minutes after announced raid
- Zulazza the Corruptor & Chizzoron the Distorter - they both spawn 30 minutes after announced raid
- Cublarc the Plunderer - it can spawn during two raids:
GREAT ORCISH MARCH - on this raid you can find 3 of them after 5, 18 and 30 minutes
ZZAIOAN RAID - on this raid you can find him after 20 minutes after announced raid (more informations where exactly he spawn you can find here)
DARASHIA:
- The Pale Count - he spawn immediately after announced raid but he has two forms and second one need to be killed to count in bosstiary
- Zomba - it spawn 5 minutes after announced raid
CARLIN:
- Willi Wasp - it spawn 5 minutes after announced raid
EDRON:
- Feroxa - it spawn only 13rd day of the month and 30 minutes after announced raid
I can also add stronger nemesis bosses that appear very rare (around 180 days for next appearing) and it is:
Ferumbras, Orshabaal, Ghazbaran, Morgaroth, The Abomination, Morshabaal, Gaz'Haragoth
And also there are nemesis bosses that spawn only during events:
Devovorga, The Mutated Pumpkin, Bane Lord (their raid is actually spawn randomly during bewitched event but still it's worth to mention them)