FINCHforum

I just ran across this list of trees and leaves that are safe or unsafe for birds. It is of more relevance to those who keep hook bills and the like that will chew on perches than to keepers of finches.
No idea of how accurate it is but it is extensive.
http://www.cbbirds.net/toxicnon-toxic.html

The list is an expansion of a list published by a landscape company in Oregon. That site has more text.
http://www.mdvaden.com/bird_page.shtml

For my uses it is confirmation that the tree branches I use for perches are all safe.

paul-inAZ As you said, the lists are more for hookbills that chew than finches, but they are still the most comprehensive lists I have seen. Always good to check and err on the safe side.

I can say from first hand experience that European White Birch (sometimes Weeping Birch) is safe for Zebra finches. Some lists had that as unsafe, but I got feedback from folks here that said it should be fine. I hung branches through the top of my larger cage, and my finches loved them. They'll perch on the tiny twig branches, pull on them all the time (of course, zebras), and pull off the leaves and seeds. I can't say how much they actually ingest, but it has to be at least a decent amount. They also really liked pulling the leaves off to use as nesting material, which I thought was heresy - all natural. It's actually time for me to cut off a few more and replace the ones in the cage, as they're almost bald now.