In order for neckwear to be visible on me, it has to be a regular tie, with no waistcoat.
http://home-and-garden.webshots.com/...ome-and-garden
Although last July, when I piped at my nephew's wedding, I just left the wing collar open, and told folks there was a bow tie under there.
I've often considered a cravat though, but towards the latter part of the year it would only push the beard a bit more forward.