British, Irish, Scottish and Welsh beer is not as heavily carbonated as American Beer and most of the head comes from air introduced when the beer is 'pulled' from the cask to the tap. This works fine, but the problem is that when these beers are bottled or canned there is no head when poured. The good people at Guinness solved that by creating the widget.
The Beer Widget-
The widget is a plastic, nitrogen-filled, sphere with a tiny hole in it that is added before the can is sealed. It floats in the beer, with the hole just slightly below the surface of the beer. When you open the can, the pressure inside drops and the compressed gas inside the sphere is quickly forced out through the tiny hole into the beer. This increases the amount of foam, or head on the beer.
The end result is that when you pour the beer into a glass you get that wonderful head so unlike the head on American beer. This head does not overflow the glass but rather cascades delightfully into the glass leaving a small foamy head on top of the beer. The beer remains unfettered with all of the unneeded gases and has a smooth taste.
Another method used, and a couple of the beers above use this, is a false bottom in the can filled with nitrogen.
But the grandaddy of widget beers is Guinness, after all, they invented it.
Started in 1759 in Dublin, Ireland, Guinness has become symbolic of Ireland. At 4.3% it is a lighter beer and lower in calories (only 125 calories for a twelve once serving). They even tout health benefits by saying, "Guinness is good for you." I run this past my wife when she starts to complain that I've had too many beers.
I discovered Guinness nearly forty years ago when it was in six ounce bottles in the local ShopRite. I've had it on and off since then, mostly when I go to an Irish place, but occasionally at home. I enjoyed a few pints in England and Ireland and the best pint I ever had was at the source when I toured the plant at Saint James Gate in Dublin. Even though there are others that I like better, I'll fall back on a Guinness often, mainly due to availability. You can get it almost anywhere.
The list is not all-inclusive, there are probably more widget beers out there that I have not yet seen. Any beer above is better than the standard mass-produced American swill and some come close to craft micro-brews. The main thing though is the non-gassy feeling after a beer or two. Try a few and see what I mean.