I remember when O'Neill's was a novelty (there must be one on every street in London these days) and all the staff were Irish, rather than Australian as they are now. They used to have really good bands on and play Irish music on the juke box otherwise (first time I've ever heard Mary Coughlan in a pub!) but now seem to have degenerated into any other chain...
Another really whacky one to visit is Waxy O'Connors off Leicester Square, W1...possibly the hugest pub I've ever been in, it has a tree in the middle of it and is decorated with the usual books, adverts, bodran's, curraghs, pulpits milk churns and cowsheds (I kid you not).