Well, first you should ask if you want a library that tries to emulate classical inheritance or one that goes more for JS's native prototypal inheritance.
DUI (the Digg User Interface library) is a jQuery addon that takes Prototype's old model and extends it in a much more intuitive way, allowing for nested static and dynamic classes, namespaces, support for the dontEnum bit and more. Documentation is available on Digg's GitHub. I think you'll find it pretty robust.
Disclosure: I work for Digg and wrote DUI ;)