I also love to head down to Cornwall's to get a "Black Velvet" (Guinness and Cider), or when I do go to England, I need to get at least one "Snake Bite Black" (Lager, Cider, and Black Currant...it is dangerously delicious).
This brings up another good point about draft (draught) vs. bottled/canned beer - Guinness is a beer I'll generally only drink on draft, where a Sam Adams I'm cool with in the bottle... I generally do prefer draft, which is why places like Cornwall's are awesome... (Sunset, Beerworks (of course) and a few others also have such a great variety) - even lesser beers seem to taste better on draft, Miller Lite, Bud Light, etc. As far as bottled goes, though the best IMO are the Ommegang Cask Conditioned beers (you'll find them at a Kappy's) - they go through a process similar to the making of a champagne, and they taste awesome...