Apart from the ubiquitous stockings on a long and curvy pair of legs, there's just something about a pair of spectacles perched on a real classy chassis that really does it for me.
Whether it's the look of sophistication, or the smouldering raunch undeneath under a demure exterior, the sort of naughty librarian / secretary I just don't know. ... it floats my boat though.
These are a few examples. There is one poster to the forum whose wife epitomises this look, but I'll leave her for him to post. Feel free to add.