From Mirrorless Rumors - http://www.mirrorlessrumors.com/zeiss-cosina-voigtlander-sigma-and-tamron-all-do-join-the-sony-nex-system/
In a flurry of activity over the past few days we have seen announcements that Zeiss, Schneider-Kreuznach and Komamura have "joined" micro-thirds in addition to Cosina-Voigtlander. Today Sony have announced that Zeiss, Cosina-Voigtlander, Sigma and Tamron are going to be "joining" the Nex system.
So it looks like we are going to be getting an expansion of what both these systems are able to offer in terms of lenses. Since both Panasonic and Sony have produced video cameras in addition to stills cameras that share the same mounts, some of what is planned is obviously destined for that. The ultra-expensive Zeiss movie lenses being an example. Zeiss is no surprise for the NEX system as they already make lenses for Sony.
The rapidly increasing sales of these compact system cameras is obviously of interest to 3rd. Party lens makers and they see an opportunity for sales and probably also don't wish to be involved in any "boat missing".
What will come out of all this in terms of products, we can only wait and see.
All this a day after Canon seemingly signaled their continuing non-involvement (non-interest?) in anything "mirrorless", with the announcement of the 600D and 1100D.
If nothing else all this should make for some interesting speculative posting over the next few days!
Sigma are going to make lenses for m4/3 as well as NEX.
From 43 Rumors - http://www.43rumors.com/sigma-announces-they-will-join-micro-four-thirds/