Barry Sonnenfeld, the director of course has confirmed that there will be MIB 3 and it will be in 3D. Oh GOD, ANOTHER ONE??!! He also confirmed what has been rumoured for months - and yes indeed Tommy Lee Jones and Will Smith will be in.
At the moment, I am not sure what is the story of the sequel will be. Sony Pictures is aiming for a Memorial Day 2011 release (end of May, around). If that so, production should starts very soon. On the plot otherwise, I can only tell you that in most likely, it will again concentrates on the bounty hunting for bad aliens (well as usual don't it). well of course, ther eis nothing comparable when you have the partner in crime - Agent Jay (smith) and Agent Kay (Jones) up on apprehending more humour and troubles. Ah, did anyone read about the pug somewhere? That little guy, I don't know if he will be in this flick though.