In addition to the ones I mentioned a while ago, here are some American breweries that I've tried and like very much. Not exactly favourites but certainly ones I'd drink if I was stranded on a desert island with a lot of beer.
New Glarus - Love Moon Man
Stone - Ruination is the only I have had
Laguanitas - Had an IPA, can't recall the name but it was very good
Goose Island - Yes, I know they're owned by the big guys but I really like Matilda
Lazy Monk - drove 4 hours out of my way to get that last year, the O'fest was worth the trip
Surly - had a couple of those in Minnesota and will have a couple more
Shorts - except that their labels are welded to the friggin' bottles which makes re-use a real pain
As for favourites:
Muskoka brewery - Cream Ale and Mad Tom IPA are great
Flying Monkeys - first "American style" IPA/APA brewer around here
Creemore Springs - now owned by Molson/Coors but the quality seems to still be very good
Sleeman - now owned by Sapporo but the Cream Ale is still pretty good on a hot day.
Wellington - Arkell Best Bitter - Friggin' awesome. County Ale - Michael Jackson gave it 5/5 and he was being a bit tough on it.
Neustadt - Very good (and my friends son works there so I have to put it on the list)
Big Rock - Alberta's finest. Traditional is great, Warthog is good, Grasshopper is fantastic
Steam Whistle - Do one thing, really really well.
But, of course none of them compare with my homebrew.