The Public Domain may not be growing (thanks to endless retroactive copyright term extensions) but it still contains a "whopping plentitude." The biggest challenge to users is simply discovering PD works in the first place. Fortunately the Open Knowledge Foundation (one of the best Free Culture organizations anywhere) has just given everyone a leg up with its new web site, the Public Domain Review. From their About page:
The Public Domain Review aspires to become a bounteous gateway into the whopping plenitude that is the public domain, helping our readers to explore this rich terrain by surfacing unusual and obscure works, and offering fresh reflections and unfamiliar angles on material which is more well known.
Go there to find all kinds of delicious images, texts, sounds, and other treasures that, thanks to our collective cultural amnesia, are as fresh and exciting as anything Big Media tries forcing down our throats today.