TJ's exclusive/private-label beers are contract-brewed by the following breweries:
Gordon-Biersch - Hofbrau Bock, Vienna Lager, Bohemian Lager, Bavarian Hefeweizen, Oktoberfest, and Winterfest
Goose Island - Black Toad, Stockyard, and Trinity
August Schell - Frugal Joe's, Gila Monster, Fat Weasel, and Jumping Cow
Vintage Ale - Unibroue
I am not sure if there are any additional private-label beers available in other regions, but those are the ones available in the Northeast. There are a few more in the works, from what I hear. As to the quality of the GB-brewed beers, I think they're good for the price ($5.49 in MA), better than Bud at the same price, but nothing worth raving about. The annual release of Vintage Ale is an event of note, however.
And may I second that comment, the Vintage Ale being an event of note! The 2008 release is super - such a wonderful blend of flavors! Complex yet every note clear as a bell. I was blown away by the bottle I had a couple days ago. What makes me a believer is how FRESH it tastes. I am no beer or ale expert, but I can only say my palate loves a beer that's been brewed especially for the season, and hasn't been sitting around! Cheers!!!
Here in California Trader Joe's are selling Gordon Biersch as there own label, maybe thats nationwide, or maybe they are using other brewers for different locations?
That being said I've tried the Vienna lager and Hefewizen. the later is fairly decent (and I believ brewed exclusively for Trader Joe's???) the former did nothing for me.