I spent a few days in the Galapagos Islands in February just before Seattle Audubon's birding trip on mainland Ecuador.
I was fortunate enough to be able to find a copy of the now out of print "Fieldbook of the Birds of Ecuador including the Galapagos Islands" by Miles McMullan and Lelis Navarette, which is a great book indeed. For you Trileigh, I'd be happy to have you come to the Seattle Audubon office and scan the relevant Galapagos pages if you wish!

In terms of IDing the finches, naturally they are dispersed geographically, with some species only found on certain islands. You can download full checklists (Excel files) from the Charles Darwin Foundation website (http://www.darwinfoundation.org/datazone/checklists/) which provide up to date nomenclature and distribution of the birds (in fact all verts, inverts, fungi and flora). I've been using those checklists a lot as I go through my images from the trip.

I hope that helps.

Toby Ross
Science Manager
Seattle Audubon Society