What plugins you will consider must-have depends heavily on your use case.
Must-have plugins if you need more power in creating advanced wiki pages:
- GraphvizPlugin
- WikiExtrasPlugin
Must-have plugins if you like IDE-style auto-completion and indentation features in the text editor:
- TextareaKeyBindingsPlugin
- WikiAutoCompletePlugin
Must-have plugins if you use many Mercurial repositories:
- MercurialPlugin
- HgDirManagerPlugin
Must-have plugins if you ...
- ... want to archive emails: MailArchivePlugin
- ... want to track time spent on tasks: TimeTrackingPlugin
- ... want to plan your week: WeekPlanPlugin
- ... want to drag cards between stacks: CardsPlugin
- ...
But if you don't have these use cases, you will not find the plugins valuable.