There is a nice bit on them under the entry for "curses" in the OCD. It seems a large number of the Latin examples were found in Britain.

Chapter 10 in a book I just got, Magic, Witchcraft and Ghosts in the Greek and Roman Worlds: A Sourcebook by Daniel Ogden (OUP, 2002)is devoted to curses and curse tablets. There is even a photo of one from Bath. It also notes, as I had recalled, that curse tablets were involved in the death of Germanicus in 19 AD (see Tacitus, Annals 2.69). The texts of several such tablets are also in the chapter.