With the recent annoucment Thanos will appear in Guardians of the Galaxy and The Avengers 2, many wonder who should voice him. Jim Starlin suggested Arnold Schwarzenneger. I do like Arnold as an actor, but not for Thanos. The actors I've selected have had some memorable roles in film, some even in comic book movies. I'll list them and two of their most well known roles, wether they're acting or voicing. These won't be in any specific order, that way you all can decide for yourselves.
Clancy Brown
Roles: Lex Luthor (DC animated films) and Mr. Krabs (Spongebob)
Liam Neeson
Roles: Ra's al Ghul (Batman Begins) and Qui-Gon Jinn (Star Wars: Episode 1: The Phantom Menace)
James Earl Jones
Roles: Darth Vader (Star Wars) and Mufasa (The Lion King)
Dennis Haysbert
Roles: Pedro Cerrano (Major League) and Jonas Blane (The Unit)
Alan Rickman
Roles: Hans Gruber (Die Hard) and Severus Snape (Harry Potter)
Kelsey Grammer
Roles: Sideshow Bob (The Simpsons) and Beast (X Men: The Last Stand)
Tony Todd
Roles: Candyman (Candyman) and Reverend Zombie (Hatchet)
Christopher Walken
Roles : Max Shreck (Batman Returns) and Captain Koons (Pulp Fiction)
Laurence Fishburne
Roles: Morpheous (The Matrix) and Noland (Predators)
Christopher Judge
Roles: Teal'c (Stargate SG-1) and Magneto (X men: Evolution)
Javier Bardem
Roles: Anton Chigurh (No Country for Old Men) and Felipe (Eat Pray Love)
Jeffery Dean Morgan
Roles: Comedian (Watchmen) and Denny Dequette (Grey's Anatomy)
Kevin Grevoix
Roles: Raze (Underworld) and Pineal Eye(Men in Black II)
Billy Zane
Roles: Hughie (Dead Calm) and Caldeon Hockley (Titanic)
Russell Crowe
Roles: Ben Wade (3:10) and Terry Thorne (Proof of Life)
Tim Curry
Roles: Lord of Darkness (Legend) and The Goblin King (Scooby Doo and the Goblin King)
Gerard Butler
Roles: King Leonidas (300) and Stoick the Vast (How to Train Your Dragon)
Ron Perlman
Roles: Hellboy (Hellboy) and Slade (Teen Titans)
Jeremy Irons
Roles: Scar (The Lion King) and Cauldron (Once Upon a Halloween)
Keith David
Roles: Dr. Facilier (The Princess and the Frog) and Goliath (Gargoyals)
Doug Bradley
Pinhead (Hellraiser) and The Doctor (Jack Falls)
Well, that's all the actors that would give Thanos a great voice. Now, you all can decide.