AS far as know only ITVN is contractually allowed to show the Ekstraklasa in the US, and they are only available on the DISH NETWORK via satellite. However, I can't confirm it, as when I tried to have DISH installed in my house (for the sole purpose of watching Polish soccer), it turned out that the trees and the mountains were blocking the signal. So, of course, there is another option: sopcast and justin tv. You can watch virtually any Ekstraklasa game, although the quality sucks.
Yep. I second that, watched Tomciotv channel on justin tv, and the quality was really good last weekend.
If you want a legit TV try polsky.tv. Little expensive but they have polish Canal+ and they have their rights to all games. If you want it for free there are more than dozen of sites that have streams. Basic google search gives you some sites meczenazywo dot pl or meczyki dot pl
Official Ekstraklasa SA channel for fans based outside of Poland: http://www.dailymotion.com/Ekstraklasa