Trader Joe's fans can lay their fears to rest, at least when it comes to beer and wine. I'm still waiting on confirmation from TJ's (the chains are loathe to divulge the name of their producers, often for contract reasons), but according to various members of Beer Advocate, TJ's relies on some well-known and reliable brewers for their beer. These are craft brewers, whose tendency is towards flavorful, quality brews.
Trader Joe's Vintage Ale 2006: This Belgian-style ale is supposedly brewed by the lovely folks at Unibroue, a well-respected Canadian brewery known for Belgian styles like their La Fin du Monde and Trois Pistoles. I picked up a bottle recently, but have yet to try it.
Stockyard Stout: Apparently produced by Goose Island in Chicago.
Trader Joe's WinterFest & Hefeweizen: The packaging (and San Jose production address) has most folks sure that these house brand beers are brewed by Gordon Biersch.
Jumping Cow Amber Ale & Fat Weasel: Identified as being brewed by Firestone-Walker, also in California.
What about wine? It's inevitable that Trader Joe's does the same with wineries, particularly given their wide selection in most locations and competitive prices. The store's most famous wine is "Two Buck Chuck," a generally lousy wine sold exclusively at Trader Joe's and manufactured by the, shall we say, controversial winemaker Bronco Wine. Turning up the wineries who produce TJ's private labels has proved challenging—in an industry where repuation is closely intertwined with cost, winemakers don't necessarily want to be associated with value-priced wine. This may change as consumers continue to educate themselves about quality wine and realize that price is not necessaily an indicator of quality.
In the meantime, if you know of any breweries or wineries producing products for Trader Joe's, please share. Make sure you let me know if it's speculation on your part, or if you have info that I don't.