Rabbotine
This is the prop which Gary Dunn uses to such good effect on his DVD - Keep Them Laughing.
Basically, it's a folder - about 8.5" x 6" (21 x 15cms) which will handily vanish a silk up to 18" (45cms). You can also switch a card, making this a really versatile prop - and it's been beautifully made in PVC to last a lifetime!