Lloyd's Of London
Lloyd's is an insurance market; moreover, it is London's, and indeed the world's, foremost insurance market. Lloyd's is not an insurer itself - rather, it is a place where those with risk and those willing to underwrite it can come together. Its precise workings are byzantine (see this Wikipedia article), involving clients, brokers, agents and members (the latter organised into syndicates), all of whom give each other money and sign bits of paper (or possibly vice versa - but not at the same time). The fact that nobody really understands how Lloyd's works is one of the key reasons why the City is still the world's major financial centre.
Lloyd's began around 1688 in Edward Lloyd's coffeeshop, which was popular with those involved in the shipping industry, and became a de facto insurance market. A few moves, acts of parliament and centuries later, it finds itself still going strong. Lloyd's is now located in its famous building, though much of the underwriting operation takes place in the London Underwriting Centre in Minster Court; Lloyd's does not sell coffee.