That's a tough one. There's so much good beer out there.
If I had to pick one favorite, it would be Okocim Porter, from Poland. Contrary to popular sentiment, I've never been of the opinion that beer travels very well, and for me to be willing to drink an import from halfway around the world is a testament to how much I regard this brand. However, the bottles are a little large for my taste, and the price is a little high. I only drink it on special occasions.
Another import that hasn't failed me yet (and comes in more manageable bottles) is Troublette, from the Brasserie Caracole, in Belgium. Troublette is a witbier, I think.
My favorite at-home beer is canned (not bottled) Sapporo. The stuff I drink here in Washington is brewed in Ontario, so it's not like it's flying across the Pacific Ocean to reach me.
When I'm at a bar, I'll go with the amber or red ale on tap, as long as it's not Mac and Jack's or Men's Room Red. I'm not sure what it's currently like elsewhere, but around here, it's hard to find a bar that will carry even one each of an amber, a porter, and a stout, while it's equally hard to find a bar that will have anything less than three IPAs on tap.
I'll put a word in for the Trader Joe's Vintage Ale, but the results are different every year. The 2009 and 2010 were both good, I thought, reminiscent of Okocim Porter. Who knows what 2011 will be like?