The Cheltenham Science Festival is a remarkable experience and I enjoyed it thoroughly. I was involved with 4 events and there only 2 nights, but also managed to catch a lot of other events. Here's a photo summary, followed by a Flickr Set.
Greg Foot, Science Daredevil (the next Brian Cox)
Professor Jim Al-Khalili, Physicist Extraordinaire
Professor Lord Robert Winston, Godfather of British Science Communication
Professor Kathy Sykes, Festival Director
Professor Mark Lythgoe, Festival Director
Alan Moore, Watch Man
Iain Sinclair, Psychogeographer
Professor Simon Baron-Cohen, not Ali G, the other one
and here's the full Flickr Set with many more people...