When our local got Bass on tap after having had Guinness already for years, I tried my hardest to teach the Iranian bartender (and owner) how to make Black & Tan. Alas, I was unsuccessful. He just couldn't get the layers to separate and always ended up with a mixed-up mess, in spite of me showing him how to do it. Anyway, he declared it impossible and gave up.

Fast-forward, MONTHS later, I walk in to find someone drinking what else? A Black & Tan. Seems that he finally learned how to make 'em... They're certainly not my favourite drink, but I will have one from time to time.

But in terms of variants... How about the pousse-café? It's not beer, but it's certainly a layered drink...