This is a tough one, because I love to go out to a bar like Sunset, and just try random stuff, and I am always finding new good ones, that I never remember about. But here are some of my old standbys (in no particular order).
-Guinness
-Leinie's (great in the summer)
-Sam Adams (I like most of the seasonals, as well as the Lager)
-Fuller's London Pride (I have gone to London the last couple of years and really nothing compares to just about any English Ale on tap)
-Fuller's ESB
-Youngs Chocolate Stout
-Hoegarrten (sp???)
-UFO
-Blue Moon
edit: I completely forgot about Victory Golden Monkee...one of my favorites lately
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).