Black garlic has been available in the UK for a while via mail order and in a few select shops. (It is used fairly widely in parts of Asia, I first had it in Thailand) It's a great ingredient to play with.
It's basically a fermented garlic bulb that gives the flavour of normal garlic, allbeit milder and IMHO much sweeter. It's fantastic to eat raw, straight from the bulb and can be interesting in marinades, sauces, glazes and wet rubs.
As it's now being stocked in a supermarket, hopefully the price will come down. It's well worth trying though. Here's the wikipedia page for anyone interested in finding out more http://en.wikipedia.org/wiki/Black_garlic_%28food%29