The U.S. has some great microbreweries! My favorites are Great Divide, Founder's, Rogue, and Highland brewing. As for mainstream beers, they all pretty much suck, EXCEPT for Sam Adams. They make some great, affordable beers. My favorite is their Cream Stout
I have to say that no American beers come close to the bottle of Belgian Westvleteren 12 that I had (undisputed #1 in the world according to beer enthusiasts). That beer was so good I literally almost shed a tear.