I am looking for a website or websites which feature found objects,
particularly pebbles or small stones but also driftwood, which look
uncannily like something or someone. Not just rude parts of the body!

You might be interest in photos of driftwood made by Sulwyn Evans, but
I have only found three on the web, several times.
Also Edward Weston:
http://www.tfaoi.com/aa/1aa/1aa503.htm

Have you searched images for "driftwood"?

Your question makes me think of the Play with Your Food books and calendars.

http://www.4to40.com/fastforward/index.asp?article=fastforward_may2001_letsplaywithyourfood

http://www.amazon.com/exec/obidos/tg/detail/-/1556706308/102-8101175-8940945?v=glance

http://www.amazon.com/exec/obidos/search-handle-url/index=books&field-author-exact=Saxton%20Freymann&rank=-relevance%2C%2Bavailability%2C-daterank/102-8101175-8940945


Looking for pictures of Play with Your Food turned up one of my
favorite posters -- Don't Play with Your Food.

http://www.artgator.com/uploads/images/adl/jpgs/S-JD015.jpg
http://www.swapmeetdave.com/Humor/Cats/CatAndMouse.jpg

I have done some searches and found the odd image here and there but
what I want is a site where some crazy fool has collected a whole lot
together. Ideally pebbles.

Thanks for the play with you food stuff. Not quite what I am looking
for but coincidentally it is the kind of thing my wife is into. She
makes tiles from casts of fruit and does projects with school children
where they make faces using bits of her casts. Her inspiration was
Arcimboldo.
http://www.illumin.co.uk/svank/biog/arcim/arcidx.html
http://www.angelaevans.co.uk/fruit.veg.shtml

Try this (Virgin Mary Toast and Elvis Toast)
http://p2pnet.net/story/3032

ebay turning toast into bread...