This name for this pitch black beer goes back to the Russian Tsar who awarded the imperial warrant to a beer exporter who had earned favor with the court by donating beer to fortify Russian soldiers wounded in the Crimea. Stephen Beaumont, author of the Premium Beer Drinker's Guide, recommends these brands:

World-Wide Stout from Dogfish Head Brewery in Delaware: at 18% alcohol, this one is for sipping.

Old Rasputin Imperial Stout from North Coast Brewing Company: pairs well with beef dishes.

Sam Smith Imperial Stout: a well-rounded, intense stout with 7% alcohol.