We have long known that some frogs are poisonous, excreting toxins from their skin to deter preditors from snacking on them. However, two are now considered venomous!
A recent paper entitled "Venomous Frogs Use Heads as Weapons", describes two Brazilian frogs; Greening's frog (Corythomantis greeningi) and Bruno's casque-headed frog (Aparasphenodon brunoi), that don't only produce toxins, but also have spikes growing out of their heads that could pierce a predators skin. This combination of toxin + spikes shifts the frogs status from poisonous, which require the frogs toxins to be ingested, to venomous, as the spikes act as a rudimentary delivery system capable of introducing the toxins directly into the victims body.
What is even more impressive is the strength of the toxins these little guys produce. The Greening's frog toxin is 2-fold more deadly than the venomous pitviper genus Bothrops, and Bruno's casque-headed frog is a whooping 25-fold more!!! So despite the frogs not having the sophisticated fangs and injection system as the Brazilian pitviper, it could still pack a punch!
The authors note that the presence of the spikes is not a unique trait to these two frogs, but it is the first documented case of them in combination with strong toxins. It is very likely that there are other venomous amphibians out there. You've got to love evolution! :)