I've recent bought this product: http://www.lovehoney.co.uk/product.cfm?p=25441 .
It seems to be working very well to keep the foreskin back. (I've cut the "dividing" bit, I'm not valiant enough to maintain that sort of kinky activity)
The hole for the penis is actually quite large, for me it's not very effective for when I'm flaccid. However, as I have at least an inch of extra foreskin past my glans (very, very long foreskin), it bunches up and bulks out the hole a bit!
looks interesting