I once saw a TV advertisement for a product called
Climatique that is supposed to stimulate the nerve endings on the woman's vulva (if I remember correctly). I think it is applied like lube but will stimulate a woman so much that she's guaranteed an orgasm every time.
Go to
http://www.climatique.tv to check it out, and also check out their FAQ link at
http://store.yahoo.com/climatique/info.html and hopefully it might be the thing you and your wife need.