Paul McGann - he played a distant relative of mine (Percy Topliss) and when I told him, he spent a good 5 minutes chatting away to us like old friends, a really lovely down to earth guy. If it wasn't for me worry about the queue behind me I'm sure the chat would gone on for a while longer.
Also the author Kit (can't remember his surname), we were waiting for my daughter to get her book signed and we were stood by his table and we chatted for a good 15-20 minutes. Was really nice.