First, to clear things up on the Colorado.
They are built here in Shreveport, LA, in a GM plant alongside the Hummer H3 and new 09 H3T. Yes, they also built the Isuzu version here but they don't make that one anymore.
I have a Colorado and it has been a solid, but yes, cheap truck. Mine is an 06 5 cylinder and it has not had a moment's trouble. The only glaringly bad aspect was some of the interior trim strip around the windshield bubbled up on mine. Yes, the external body components are thin and it's not a truck to lean against. But at the same time, I wouldn't say the sheet metal feels any thinner than that on my CR-V.
As for the Malibu, a co-worker of mine has an 08 4 cylinder 4 speed auto and can't stop praising it. He does mainly highway driving and without any particular gas-saving techniques other than driving the speed limit, his highway mileage hovers around 38 mpg. I've sat in the car and it seems very solid. Maybe one or two of the trim pieces on the dash are a bit harder plastic than I like. But they still don't scream cheap and it's still VASTLY improved over GM models past.... One thing I would say, though, is it seems a bit tighter inside than say, a new accord. But I could easily see myself driving one, especially the v-6.
But honestly, if I were to buy a car in the $20k range from GM right now, it would be the Cobalt SS. Especially after Road and Track put it up against the mazda 3, WRX, and Lacer Ralliart and ranked it first.
http://www.roadandtrack.com/article.asp?section_id=31&article_id=7103