Duvel's a good shout. Definitely among the best beers easily available in the UK; i.e. stocked by supermarkets and a fair few bars. The Belgians make better beer than Duvel, mind you. Sadly, the only Belgian beers you really see are Leffe and Hoegaarden (ruined by InBev). It's a shame because Belgium is one of the few countries whose brewing heritage matches our own - not that we pay attention to it, as this thread proves.
If anyone ever visits Brussels - stop off at Delirium Café, Les Halles Saint-Gery, Mappa Mundo...