Walls: Aegislash Ex, Suicune (Expanded), Raikou, Regice, Sigilyph (expanded), Wailord EX, Primal Groudon, Regirock Promo, Pyroar, Beautifly, Robo sub swarm, focus sashed pokes, Crustle, Assault Vested Mega, Hippowdon
Now I may have forgotten a couple but those are the major walls, each with different levels of viability.
Tiers:
S: None
A+ = Assault Vested Pokes/Assault Vested Megas - Don't be surprised to see a couple of decks that perform well running assault vest, makes numbers hard for your opponent and gives you a good attacking option. Wailord Ex - Nearly nothing can one shot it outside of Vespiquen, an easy wall to throw in and has the potential for future decks revolving around it with Golduck Break. Robo Subs - very little drawback besides taking space in the deck, synergy with teammates is nice too - Great for hit and run decks, although those seem to have waned a bit
A: Primal Groudon - With the speed of the current speedy meta Primal Groudon has fallen a bit off of anyone's mind, but with something like Golduck break Primal Groudon could become a fearsome beast once again. Focus Sashed Pokes: Focus sash is a great card that can help any deck wall a little, obviously helps something with an omega barrier even more.
A- Raikou: A bulky and hard hitting one prize attacker, decent currently.
B+: Aegislash-EX, Suicune, Sigilyph. There aren't many decks that can use these effectively currently [Tyrantrum would rather be using Tyrantrum or Giratina as the main attacker] and with hex maniac being a staple,
B: Hippo and Regice: Obviously Hippo and Regice are great in an ex meta, but with too much non-ex they become mediocre walls. Regirock Promo - a safe and easy bench wall, doesn't see much use though because not many decks can use it effectively. I think it has more potential with something like delinquent and sash in standard than people realize though.
C: Anything else. Make a name for yaself other walls