Hipikat looks like an interesting Eclipse plugin. It's a research project that provides pervasive search of your "software artifcats"...documentation, bug notes, news group posts. Check out the senarios for examples of its use. It's a research project and obviously a little flaky, but the ideas are cool.

This reminds me of an idea I had for a searchable and editable "Developer's Notebook" which would be sort of a rich client interface to a wiki, with diagramming and documentation generation capabilities. Perhaps something like that would be a good Eclipse plugin as well.