The smallest usable poncho I've found, after a very long search indeed over a good few years, is the Tenth Wonder jobby; it's small, very light and does the job very well. However, the smallest I can get it to pack if I try to compress it down is about the size of a 1 litre Nalgene, so I dont bother, I just put it away loosely and nestle my other gear in, on and around it.
Anyone carry one, Im looking for something that packs down real small for my just in ca^^%se kit, the highlander one looks good but Im not sure how small it packs?
Something the size of a space blanket folded would be ideal