My favorite beer if from a New Hampshire brewery called Magic Hat; their #9 brew, a "not quite pale ale." It actually gets its flavor from apricots You can't get it outside of New England AFAIK.
Wachusett, a Massachusetts brewery, has an excellent repertoire of beers; their blueberry beer is famous.
Second to that, pretty much anything Sam Adams makes that doesn't have "black" or "brown" in its name. I've heard that outside of New England the quality degrades - but I find that hard to believe due to my next favorite beer.
Heineken! It's the world beer. You can go to any part of any country, go in to any bar, order an Heineken, and you know it was brewed in Holland. Very few international beers can say that. Along the same lines as Heineken is Newcastle Brown Ale, which has already been mentioned - they are very similar beers, though Newcastle is darker.
Guinness is always a favorite, but it'll fill you up like thanksgiving dinner. I'm partial to Black&Blues, which means Guinness floated over Wachusett Blueberry (it's a local thing, for a local beer - based on black&tan, which is Guinness over Smithwicks [read: Smiddicks], or sometimes nontraditionally Bass)
