1/2 a pint of beer. Brits like to use lager, in the States we seem to use Guinness more. I guess we think it's more "authentic." For craft brew lovers, try Old #38 Stout from North Coast Brewing Co., or Black Sun Stout from Three Floyds Brewing Company.
1/2 a pint of hard cider, such as Woodchuck or Strongbow.
a dash of blackcurrant syrup (optional)
Pour into the same glass. If you want to get really fancy, use the back-of-the-spoon method. Turn a spoon upside-down over the beer and gently pour the cider over the back of the spoon. This allows the cider to pour down the edge of the glass and rest on top of the beer in a pousse-cafe layering..