I recently swapped a duplicate photobook with my pal Bjorn for his Contax TLA140 flash that he was using with his Contax G1 before he upgraded to the TLA200 version. It’s a simple little manual flash that is powered by one CR123A battery and while it doesn’t cycle very quickly it is smaller and more unobtrusive than the Leica SF 20 flash that I usually use. These flashes are pretty common and cheap on the used market in Tokyo- I saw about four or five at Kitamura Camera in Akihabara last week for about 2900 yen ($30 USD) each.
Best of all is its design- a blunt little utilitarian rectangle that lights up your pictures.