These are all members that have been in the Akatsuki at a time, if they are current, deceased, etc. all of them.
*The member list from the wiki. *

1. Orochimaru
Completely brought back 4 Hokage from the Reaper Death Seal, Co-Inventor of Edo Tensei. 1/3 of the Legendary Sannin, could be a major villan for a second time after the war(or during it.)

2. Obito
The "main" villan at this moment. He is controlling the Juubi all by himself.

3. Nagato
Completely destroyed Konoha, almost beat Naruto and Killer Bee. And possibly would've if Itachi didn't save them. He showed many more jutsu after he was reincarnated, I wish we would've saw more of Nagato.

4. Itachi
One of the best Genjutsu manipulators, and was "unbeatable" in Part 1. Until he got sick and died from Sasuke.

5. Konan
Almost took down Tobi(before he was Obito)like it was nothing, something a whole army isn't able to do.

6. Zetsu
Many clones, 'Hashirama' clone, "unbeatable."

7. Sasori
The puppet GOD, nearly killing Chiyo, Sakura, and Kankuro. 3 very good shinobi.

8. Deidara
Need I say more if you saw the Sasuke fight?

9. Kisame
One of the 7 Legendary Swordsmen, needed a 7th Gate Might Guy to kill him, and almost killed Killer Bee.

10. Kakuzu
Unless having all 5 hearts destroyed at once, he wouldn't have died. Was pretty badass when he was alive.

11. Hidan
Needed a long time to set-up a ritual(that kills anyone with blood on his 'special' sword,) one of his pros and cons.

12. Yahiko
We never saw "Yahiko" as Yahiko, just as the main Pain. Not what we could see, I wish I could've seen more.

*This is MY list, not yours, we all have different opinions.*