It's been confirmed that Kat Dennings will be returning to reprise her role as taser queen Darcy Lewis, thankfully making her among many of the actors who will also be returning. Others so far include:
Natalie Portman - Jane Foster
Chris Hemsworth - Thor (obvious, really)
Tom Hiddleston - Loki
Anthony Hopkins - Odin
Rene Russo - Frigga, Odin's wife
Idris Elba - Heimdall
Stellen Skarsgard - Dr. Selvig
Ray Stevenson - Volstagg of the Warriors Three
And while we're on the Warriors Three topic, Fandral (the one that looked like Robin Hood) is set to be played by a different actor. Original actor Joshua Dallas had to back out due to scheduling conflicts, and will be replaced by Zachary Levi.
Turning to new characters, it's suspected that producers have found someone to play the wife of new villain, Malekith the Accused. It's rumored that Alice Krige, whose sci-fi / fantasy credits include "Silent Hill," and "The Sorcerer's Apprentice," will play the Dark Elf Queen Alflyse.
Lastly, Adewale Akinnuoye-Agbaje (Heavy Duty from the last "G.I. Joes" movie), will take on the role of Algrim the Strong, a powerful dark elf convinced by Malekith to fight Thor.
Thor: Dark World hits theaters on November 8, 2013.