I've met a variety of people but I'm not sure how well known they would be outside the UK:
The Wombats; The Zutons; The Coral; Johnny Wilkinson; Dave Spikey; Steven Gerrard; Emma Watson; And then the vast majority of UK politicians(inc. Gordon Brown, Tony Blair, Ed Miliband, William Hague, Ken Clarke, Vince Cable)
I met Lita, a professional wrestler that I was a fan of when I was younger. I was speechless when I did, couldn't say anything. I haven't met anyone else special =/