I like Mimi Rogers EVERYTHING, but would probably not classify her as a geek or nerd... even when she's in a role of a scientist/investigator (Forbidden Planet, X-Files) her personna is still essentially mature (wonderfully) glam.
Yes, some of the references above ARE of idealized Hollywood geeks, where as was pointed out, an attractive actress is dressed down specifically to be 'outed' later in all her glory. Some watering down of the genre is probably inevitable given our need to use common references (actresses, models) in order to communicate efficiently.
To me, though I like glasses on pretty much any woman, a woman is not a nerdette simply because she wears glasses. She must have many of the other qualities described above: intelligence, preferably an interest in something technical (science, technology, etc...), modest almost anti-glam dress, hair and makeup, an apparent lack of concern/awareness of the fact that she may be very desirable, etc....