Mads Mikkelsen, who I hope you know best from films like Pusher and Valhalla Rising, is in talks to play a villain in Thor 2, which films later this summer. Who is the villain? Nobody knows!
The rumors have been that The Enchantress would be in the new film, and where The Enchantres goes she's often followed by The Executioner, Skurge. The Enchantress, for those who did better things with their youths, is a foxy Asgardian sorceroress whose specialties include mind control and illusion. In her first appearance she was sent by Odin to seduce Thor away from Jane Foster, whom the All-Father felt was a distraction. The powerful Executioner, who is in love with her and whom she strings along with her boobs and gams, is on hand to actually off Jane. They don't succeed.
Traditionally The Executioner is a pretty beefy guy, quite unlike Mads, who tends towards the ropy. Skurge also has the most ridicuous haircut imaginable. It's possible, though, that this is who Mads is playing. It's also possible he's playing any one of a number of tertiary characters from the mythos - god knows they're going obscure in Iron Man 3, so why not here.
We do know that Loki will return in Thor 2, but how he plays into the story remains a mystery. I'm a little worried about Loki burnout, so I hope the new film - which will be directed by the talented TV titan Alan Taylor - does something interesting with him. Maybe he'll have to team up with Thor to stop a bigger threat.
If you asked me who I wanted as the villain in Thor 2 (and you're visiting my site, so you pretty much did) I'd say Surtur. He's an enormous (like, over 1000 feet tall) fire demon from one of the Nine Realms. In his first comic book appearance some really wacky shit went down - Odin stopped time and took every human off of Earth for the duration of the battle, and Thor got thrown into the sun. That would be pretty cool in a movie. I guess you need more story than just 'thousand foot tall fire monster attacks,' but those brains at Marvel could figure one out.