http://us.akinator.com/# is rather addictive, and can be surprisingly accurate, although it has odd blind spots. So far it's accurately guessed Solid Snake, Sam Vimes, Nanny Ogg, Tuco, Aeris, Madlax, the Boss, Volgin, Bertie Wooster, Naomi Hunter, Stephen Fry, Otacon, Doctor Watson, Scarlett O'Hara, and Gendo Ikari all on the first try. It did get stumped by Shinji Ikari (although that might have been from bad answers on my part, as I've only seen the first couple episodes of Eva), Brutha, Adora Belle Dearheart, the Great God Om (turtle version), Beth March (although the first guess for her was Jo), Marcus Didius Falco, and Decius Metellus of the SPQR books. It seems to do best with fairly major characters from recent nerd culture.