I'll drink just about anything that appears at the Cambridge Beer Festival. I'm sure other Festivals can be used as a guide; Cambridge is the one I'm familiar with.

But my favourites have to be Black Sheep (because it's the nearest brewery to my birthplace) and Jennings (Cumberland Ale in particular). And most of the British ones mentioned by ashmoore.

In the US, the only place I've spent much time was in Salt Lake City, Utah. There are about 3 brew pubs in the city, and I liked them all, despite the low alcohol content - they seem to compensate by being very good on taste.