We recently were introduced to a beer cocktail called The Black Velvet!
The Black Velvet is a mixture of Stout (like Guinness or Murphy's) and Cider (like Strongbow or Woodchuck). This is a dangerous combination that's super easy to make. Just fill about half your glass with cider, then pour in the dark beer over the back of a spoon. You use the spoon to help prevent the two liquids from merging. If you're successful the light and dark can be pretty distinct, as seen in the picture (ours didn't quite look like this). Oddly when you drink it the flavors remain somewhat distinct also - the stout first with a cider aftertaste.
The Black Velvet is a very tasty concoction. The stout tempers the sweetness of the cider and/or the cider spices up the stout. The first time we made these we used Guinness and Woodchuck draft cider. Then the second time we tried Murphy's and Strongbow. Both combinations went down smoothly.
There's a place near Lovingston called Albemarle CiderWorks that makes some excellent Virginia Ciders. Not far from there near Wintergreen is a great brewery called Devil's Backbone. Last time I was at Devil's Backbone they had an Irish style stout on tap called Ramsey's Draft. I would like to try mixing a growler of Ramsey's with an Albemarle Cider. I bet that would be good.
I suspect you could also use a porter like Fuller's London or one like Hampton, VA's remarkable St. George's Porter. If you're really fancy instead of the cider you can use champagne or sparkling wine. I'm not usually one to go in for beer mixtures like this, but I'm beginning to think otherwise. Cheers!