I use two Avon products: the Jillian Dempsey for Avon Professional Brow Styler, which is a crayon and gives a real Kate Middleton look, and then the Pro Brow Definer, which is a liquid dispensed through a brush. Don't put the liquid on first, though, as the crayon will take it off again! A finer crayon is the Glimmerstick Brow Definer and if the Brow Definer is unavailable, use a mascara (but not too much!) as the brush should give the right effect.
Website address below if you haven't got a local rep:
http://www.avon.uk.com