Familias Dominicanas
I forgot to mention that there is a very hard to find set of books, 12 volumes I think, called Familias Dominicanas, which detail at length Dominican families back into the 1500s. Very interesting. Each volume covers a couple of letters of the alphabet - for example, Volume 1= Surnames starting with letter "A". I have only one volume, that for O & P surnames. [3 of my husband's surnames are Pena, Olivo and Piantini]
There is a group on Rootsweb who are doing Dominican genealogy research - some very serious people there, and many of them have different volumes of Familias Dominicanas and some will do lookups for you.
AE