It appears to be confirmed: Paul Rudd has been cast as Hank Pym in the
Ant-Man movie. Since I only know Rudd as Josh from
Clueless, I am fairly neutral about this news, but of course I'm hopeful that he will be able to play Hank in all his dorky, and utterly bizarre, glory.

AFAIK neither Janet nor Scott Lang have been cast yet.
Here's my theory about how the MCU is going to go, based on what movies have been greenlit, and what little we know about them:
1.
Guardians of the Galaxy is set for an August 2014 release. I think it's pretty obviously going to be
Avengers 3, Part 1 -- this is the movie that's really going to set up Thanos for the third Avengers flick.
2.
Avengers: Age of Ultron is set for May 2015. Surprise surprise who the main baddie is. The studios keep saying that Hank isn't connected to Ultron in this continuity but I think that's a red herring. They also swore up and down Paul Rudd wasn't going to be Hank, and look what happened.
3.
Ant-Man is set for July 2015. Interestingly, the movie's release was moved up a few months from November despite the fact they didn't even have the lead actor until like this week. This suggests to me that
Ant-Man is meant to ride the wave of excitement that
Avengers: Age of Ultron is going to generate.
4. The next property that seems to have the most momentum is
Doctor Strange. That's the one Feige keeps bringing up, anyway. There also seem to be tentative plans for a
Black Panther movie and one starring a Marvel heroine (Black Widow seems to be the most likely candidate).
5. Avengers 3, which might be the untitled project with a 2017 release date (just a guess based on the amount of time between Avengers 1 and 2) is going have Thanos as the baddie with, presumably, a modified Infinity Gauntlet story.
6. With the Blade rights have reverted back to Marvel, and the success of the previous
Blade trilogy, I'd be surprised if Marvel didn't reboot that franchise as they did with Ghost Rider.
That being said, after Loki, Thanos, and Ultron, the next most iconic Avengers villain would probably be Kang the Conqueror, but putting him onscreen will probably pose a bit of a challenge, just because of his time travel schtick. You could do a Korvac saga with little problem and hell, we've already got the Collector onscreen, so just cast a Carina and go for it.