I'd say Egghead if they could do him and not make him look like a Conehead

Definitely Egghead.  

SIMON PEGG!! <3 XD

Pegg is a god. If he wants to be in your damn Avenger's movie, you find a way. make him a goofy scientist or Shield agent for crying out loud. ITS SIMON PEGG!!!
 honestly though, when any actor wants to be in these big budget movies, unless they want big bucks, you should squeeze them in. You can do it without making it a sleazy cameo. 
 Get it done Marvel.

I think making him Egghead would be good. He just needs to shave and then they could make the head egg-like by using CGI. Or he could be Scot Lang.

Ultron is british right?...right?

Well he could play The Voice or Whirlwind. >.>;;;

egghead,lol...what a stupid villian

Well he did play a okay villain in a episode of Doctor Who, so I say give it a shot.

I don't know who Egghead is but I will research him and then make my decision on him. 
EDIT: After looking at the Egghead page, I totally think he would be great as Egghead.  Having him be a mad scientist would be great.  Also, how great of a team name is the Emissaries of Evil?

No! Simon Pegg is...
The Highland Laddie

He obviously wouldn't be Ultron, but how awesome would a live-action Ultron be?

Egghead. Yep.

" Definitely Egghead.  

"

he can be serious; just look at hi role in Hot Fuzz, which was fantastic

Whirlwind is the villain they should go with for an Ant-Man movie. I just can't see Egghead as a serious villain, lol

Besides Egghead, what other Ant Man bad guys are there?

Simon Pegg is hilarious. Even in a simple interview he is able to get in some jokes! But, alas, he is correct on the whole Marvel wanting good-looking Americans... (Marvel Studios that is) to play the lead roles. Who is Ant-Man's villain though? I don't really follow the little/big guy, so the question is... Who would Simon Pegg play?

Would be pretty funny. lol

Pegg would make a decent Scott Lang. I don't see him as Pym, really, unless they reinvent the character entirely (which I'm against)
 
But if they managed to make a viable Egghead, Pegg would tear it up.
 
Heh. "Pegghead"

Whatever role he plays, they just NEED him in the movie.  I absolutely love Simon Pegg and think he can play comedy, drama, and action all equally well.  I doubt they'd make him the lead whether it were Pym, Lang, or O'Grady, but he should be in the movie.

Awesome.