My answer - the cold one in my hand.
Well, that's not entirely true, as I'm not fond of basic domestic beers (Bud, Miller, Coors, etc.).
I always loved Sam Adams, and the Sammy Light is pretty good too. I love most IPA's, and Harpoon makes a great one. Sometimes I like a nice Blueberry Ale, with fresh blueberries tossed in.
If I'm at the Mexican place, I'll get a Corona Light. If I'm at the Irish Pub, I'll get a Smithwick's if they have it, or a Guinness (or Black & Tan). We went to Ireland 4 years ago on our honeymoon and I fell in love w/ Smithwick's. Very happpy to see that it is available here in the U.S.
Unfortunately, we can't get Shiner Bock up here in Boston. I've had that a few times and loved it.
Damn, it's only 9am. I gotta wait another hour before I can have a beer??
(just kidding - I'll wait until 6pm tonite)