The standard spy camera (looks like a tiny 110 camera) is the Minox 8x11 and is still in production in various forms, from about £200. Disc cameras were noted for their ease of concealment due to their thin design, but they haven't been made for 10 years and the film is no longer in production. Best bet for availability is an APS camera- relatively small, easily available and cheap
PS - there is a small (110 size) polaroid camera (the i-Zone)
[This message has been edited by Mycroft (edited 31 January 2001).]