I believe that the great examples always arise from OpenSource projects. The design and modular code always play a great role in increasing the ability to customize or add features and also have an increase in collaboration from more volunteers.
Developer life gets more interesting with a massively improved code quality when some tough decisions are taken much earlier.
There are great examples in open source, but my main issue is open source projects are usually frameworks. Frameworks solve a lower level problem than end user application code. I often see excess abstraction and unneeded flexibility in business code that just makes the problem domain harder to understand, without ever providing value.
