Guinness extra stout is THE BEST! However...
As far as mass produced beers go...Leinenkugel makes one call Big Butt Dopplebach, Killians has one called Irish Red (not too dark, but an acceptable substitute if Guinness is unavailable), Michelobe has Amber Bach (refer to note about Irish Red). All are descent beers that won't dissapoint.

Microbrews are where it's at though. When I visit friends in Madison,WI I like to get Oscar's Chocolate and Oatmeal stout. I know it's sounds kind of gross, but it is probably the best beer ever. You almost can't go wrong with an oatmeal stout. Some friends and I plan on going to a Microbrew fest in Wisconsin in October. It's in Wisconsin Dells you should check it out if you live close enough.