This is quite a good article on dried leaves, though the author does not list all leaves good or bad; he does provide some that he has used, and warns to avoid poisonous trees/leaves. Note, he advises never to boil them, just ensure the collecting site is safe.
www.seriouslyfish.com
The same article also appeared in TFH:
Aquarium leaves may not be an obvious decoration for home tanks, but they can provide big benefits to your aquascape.
www.tfhmagazine.com
And this is another good article:
Collect fallen leaves from a nearby forest and use these to decorate your tank.
www.practicalfishkeeping.co.uk
My recollection is that leaves from deciduous hardwood trees are generally safe as far as the leaf itself is concerned. Never use coniferous/evergreen leaves or needles as these likely contain toxic substances. Some tropical leaves also contain toxins, so those who live in the habitats of our fish need to be careful.