Ones I've paid to see:
Stewart Lee, Simon Munnery, Bill Bailey, Rhys Darby, Rob Brydon, Mark Watson, Dave Gorman, Frank Sidebottom, David Sedaris (if he counts as a comedian), Mark Steel
Ones I've seen free (I used to work in entertainment PR so saw a lot of stuff for free):
Julian Clary, John Thompson, Sean Locke, Jo Brand, the Comedy Store Players, Lee Mack, Jenny Eclair, Ian Stone, loads and loads of non-famous circuit comics whose names I can't remember