OK, maybe I'm showing my age here, and perhaps she's not a classical beauty, but surely the ultimate hottie sci-fi time-travel kick-ass babe with Sonic-screwdriver, jodhpur and gun-fetish has to be Alex Kingston as River Song?

I mean, come on, she can make a Dalek beg for mercy with a look. . .
http://www.youtube.com/watch?v=c_9Y0_Uzh1oShe has the perfect outfit, side-arm and put-down for every occasion. . .
http://www.youtube.com/watch?v=QU-w82PCHqAAnd is just goddam sexy as hell. . .
http://www.youtube.com/watch?v=_rjM8rHO8f4Gotta love a woman who can handle herself
