I've never seena standard one. And be careful about signing them: one I saw recently mentuionned that, by signing the nda I agreed that the product or service had a monetary value. Which, of course I would not know until I signed the form and found out, so I could not sign it.
Like most legal documents, there are probably a few floating around.
However, they might not suit your circumstances, or may just not work. If you can afford to take the risk then use them, if you can't then go and see a solicitor.
