Examples of well written open-source plugins?

I learn best by example, so I'm looking for well written open-source JUCE plugins that I can learn from. I'm not just looking for a tutorial - partly because I already understand the basics, but mainly because I'm looking for how you should do things, not just how you can do them (not so much general C++ things, but things specific to audio plugins and JUCE). Some areas I'm particularly curious about are multithreading, resource management, and more complicated GUIs. But I'm also looking for examples of best practices in general.

So does anyone know of any good open-source plugins to learn from?