There is a site that is dedicated to streaming Cowboys games but I can't mention that site here because it is banned. Besides, you have to go thru a bunch of hoopla to even get connected to that stream anyway.
Most of the sites above are ok, but the piracy police will eventually catch on those sites and shut it down and then you will be forced to scramble for another feed. The chatrooms on Justin.tv usually keep you up to date on which streams are active.
I think your best bet for reliability would be to download
Stream Torrent and get the direct link for the live streams. This program isn't affected by the stream police somehow, but the stream is usually about 3 minutes late and doesn't have audio. I usually watch it from there and then find a radio station for the audio, but because the stream is so late, it becomes annoying and I end up trying to find a more current stream on justin.tv.
So those are pretty much your only options, unless you buy NFL ticket or find a sports bar like I plan to do this week.