[hachiya]

Interesting. I've liked Roundcube enough to use as a backup way to access mail, but I've never looked at the plugins.

What are some of the plugins that you find useful?

[thaumaturgy]

The spamassassin plugin lets you control your spam settings from your webmail account.

I also have managesieve installed, and there's a plugin for it too, so with imap, inbound email gets automatically sorted into folders for me, and I can control that from RoundCube. The filtering is actually way more powerful than anything Gmail can do (last time I checked).

Those are the two "must-haves" IMO.