According to the achievement list in Raevyn Wiki, the raid boss list is the following:
Bastion of Twilight:
1.Valiona and Theralion
2.Halfus Wyrmbreaker
3.Twilight Ascendant Council
4.Cho'gall
5.The Horrifying Secret
Blackwing Descent:
1.Magmaw
2.Dark Iron Golem Council
3.Maloriak
4.Atramedes
5.Chimaron
6.Nefarian
Skywall:
1.Djin Council (probably a mini boss)
2.Al'akir
Bastion of Twilight:
-Valiona and Theralion is a double dragon boss, there is an achievement in which you must kill them at the same time
-Wyrmbreaker is probably a gronn or an ogre looking enemy. Gronn probably because they famous for killing dragons
-Twilight Council is an Elemental council (Probably fire, water, and air elementals)
-Cho'gall is the final boss, and to my speculation the secret boss is Sinestra or... really I have no idea but it has to do with the dragon eggs.
Blackwing Descent:
-Magmaw is probably a fire worm or a two-headed fire dog. The second boss is a Golem council and as for the rest of the bosses, you can speculate according to their names.
So if you guys have any good speculation as to the bosses go ahead =)...