Newcastle's been a long standing favorite of mine.
Mackeson Triple Stout is fucking delicious. I love this stuff.
Franziskaner Dark is really, really good.
Schwarz has grown on me a lot. REALLY tasty, black beer.
Sam Adams has some good stuff, like the Boston Lager and especially the Brown Ale.
Yuengling Porter is fantastic.
As Alcapoth said, Hobgoblin is really good.
You can probably tell, I go mostly for dark beers. Sam Adams' Boston Lager and Hoegaarden are about the only exceptions I make, but I'm trying to branch out and give more types of beer a shot. I steadfastly refuse to drink Budweiser, Miller, etc. Terrible, terrible stuff.