Magic Hat has one REALLY good seasonal beer, Roxy Rolles (a well-balanced but hoppy American amber ale; almost a red-IPA, maybe not quite bitter enough). Exceptional beer, one of my favorites. Other than that, though, the best they do is medicore for stuff like Circus Boy to downright horrid for stuff like that new, beet-juice-infused summer ale I was dumn enough to buy a few weeks back.
Sam Adams, I know they have a few horrid offerings but you've got to give props to what they've done to the homebrew community, the support they offered other craft brewers through the hop crisis, and most of their beers are at the very least quite drinkable. The Black Lager is another beer that I consider exceptional, one of my favorites from ANY brewery large or small. If I had to pick a single beer to drink for the rest of my days, the SA Black Lager would be one that I'd have to think long and hard about.