I think I say the same thing in every beer-related thread, but...
To me, the Belgian ales are the best, by far. By that I don't necessarily mean from Belgium, but the styles. Any of the Trappist ales from Belgium are fantastic, and there are many other brewers that brew in the various Abbey Ale styles. Some of my favorites:
- Allagash. Everything they make is great, and they're an American brewery.
- Ommegang. Everything they make is great as well, and they are also an American brewery.
- Victory Golden Monkey. Same as above.
- Rochefort. Probably my favorite Belgian Trappist. The Rochefort 10 is so rich and complex, it might as well be wine.
- Westmalle. Another fantastic Trappist. This one is typically a little more citrusy than the Rochefort, but great body and wonderfully complex.
- Westvleteren. You won't likely find this anywhere unless you're extremely lucky (unless you go to Belgium), but it's out of this world.
- St Bernardus. A Belgian brewer that makes a lot of different ales. The Abt 12 is probably my favorite, but they have a lot of different labels/styles they produce as well. Watou is another great one.
- Konigshoven. Hard to find much of the time, but they make great dubels, tripels, etc.
There are so many more. Explore the various Belgian styles and the various brewers and you'll be busy for years.