Two I can think of off the top of my head. Both were involved in politics. They knew the issues, they knew who was in favor, who was opposed, whose minds could be changed. They knew the true cost of every piece of legislation (something which the real politicians liked to ignore), the historical background of both sides of every issues . . . and they could explain everything they knew in ways appropriate to anyone from a 5-year old to a post-doctoral fellow.
Damn. I wish I could meet some of these women.
Smart. Is. Sexy.
One of the smartest women I know is my aunt. She can sing at a professional level, does all kinds of volunteer work, reads, writes, plays the piano, and in her sixties moves faster than any two other people I know.
Another was my crush in high school: straight-A student, cheerleader, shared one of the most distracting physics lasses I have ever had with me, spoke English, French, and Japanese… there was no way I could convince myself I had any chance with her.
Another was a teacher I met, a teacher of world religions at a catholic school. She did classroom work on dozens of different religions (including neo-paganism), spoke multiple languages, sang, gardened, and had the most wonderful and poetic answering-machine messages. I would occasionally call her just to hear her messages. If more religionists could be as open-minded and passionate about their beliefs as she, I wouldn’t want to ease towards the exits everytime someone mentions God. As it was, if she had been single and interested, there’s a serious chance I would be Catholic by now. 
She once called and politely declined my request for a date, after I wrote her.
My wife is truly the smartest person I have ever met. She has a Ph. D. in Psychology and she knows so much medical stuff it is just freaky. She has worked in several hospitals and picked up lots from there but she also reads up on lots of things.
Then there is her general knowledge. We watch Jeopardy! on tv every night and I am always really impressed with the things she knows.
[sub]And of course she decided to marry me too.[/sub] 
Several. But I can tell you that I met Raquel Welch once, and she was VERY smart. Not to mention friendly and gracious. And, lovely.
I think the smartest woman I’ve ever met is my friend Mary. She used to be in IT, on the networking side of things. We met working a short-term contract here in town, upgrading computers for Sprint. This was after they’d done a lot of downsizing and it wasn’t a good time to be a tech, so there were a lot of us who couldn’t do any better than contract work. She was easily one of the two best techs there and, in fact, one of the best I’ve ever worked with.
She was pretty, but she was awfully quiet; like a lot of women, it seems, she has a low-opinion of herself. Made worse by her last husband: several years ago, he’d caved in parts of her skull and broke her back and left her for dead. When I met her, she’d been in severe pain for a number of years, despite being on ungodly strong meds.
The meds and the pain are taking their toll on her: she slurs her speech a lot and has trouble focusing on things. She’s not as sharp now as she was when we met, and I can only imagine how bright she was before, but she’s still the smartest woman I’ve ever met, even if it doesn’t show so much anymore.