Black box and delicato are both considered as good as any mid-priced bottle wine.
The cheapos at the supermarket are not that good but they're comparable to any two-buck-chuck type wines.
I've liked the Corbett Canyon merlot in the 3 liter box. Their whites arent too bad.
I've noticed the "better" wines tend to come in a 3 liter box while the cheaper ones come in 5 liter boxes.
The Corbett Canyon is a regular here at our household. I use it for cooking and occasionally even drink it with a meal.
If i'm going upscale a little, I do like the Yellowtail's that Cut-Throat originally turned me on to. The local sams club now carries a variety of theirs for under $6 for a 1.5l bottle.
If you have a trader joes nearby, try their charles shaw Shiraz. It recently was named as a top wine in america in a blind taste testing. The broad set of tasters were so appalled that they chose a two buck chuck wine that they thought their reputations would be ruined. I've tried it. Its pretty darn good.
http://www.signonsandiego.com/uniontrib/20040617/news_1n17wine.html
Wine is a different business now. The low end has really, really improved. I live within a few hours of most of the larger 'wine country' areas. I've noticed that almost all the farms are now growing wine grapes to some degree. There was a news spot on the other night talking to smaller farmers who are giving up carrots and tomatoes for wine grapes and making a lot more money.
So any talk of the 'wine glut' ending and the end of the supercheap wines is whistling past the graveyard if you ask me...