Pylearn2 seems to be the library of choice, however I find their YAML configuration files off-putting.
Python itself was designed to be an easy language for prototyping, why would you not use it to define the network properties themselves? We have great editors with autocompletion that would make your life much easier and Python is not like C++ where you have to wait for long builds to finish before you can run your code.
YAML files on the other hand you have to edit using a standard text editor with no assistance whatsoever and this makes the learning curve even steeper.
I may be missing the big picture but I still don't understand what were they thinking, I don't think prototyping in code would be much slower. For that reason I'm considering Theanets or using Theano directly.