Rupert Gethin, President of the PTS, has just announced that the first three volumes of the A Dictionary of Pali (collated by Margaret Cone), are now available to search free online via Gandhari.org β
Vol. 4, which will be the last, is being prepared by Martin Straube (for reasons that are not entirely clear, Cone cut all connections with the PTS after Vol III appeared).
Personally, I still find Rhys Davids and Stede dictionary serviceable for day to day use, but DOP is much more accurate and goes much deeper. When constructing her entries, Dr Cone would literally look at every single occurrence of the word in the PΔli Canon and that in several editions.