That old question of "If you could have dinner with anyone at all, living or dead, who would you choose?"
My answer has always been Oscar Wilde, who just seems like he'd be the best host for this imaginary dinner party. Since we're imagining, I'm also going to assume that there are no language barriers, either. Some of these guests may not actually be fun in real life, but it would be fascinating to listen to them all talking to each other:
Xavier de Maistre
Leonardo da Vinci
Lord Byron (the young version)
Who have I left out? I'm sure there are many....