Eclipse Resource Tagger Plug-in - The Resource Tagger Plug-in adds tagging functionality to Eclipse such that resources may be tagged similar to the content tagging in Del.icio.us and Gmail. The tagged resources may then be managed, searched, filtered, or otherwise operated on by their tag associations.

This is another one of my development projects. It is pretty much a dead end as I have found ways to use Working Sets to remove the need for it. If you are looking for tagging in Eclipse you should look into TagSea which is still under active development.