Which modules should I add to Advanced Forum to provide increased functionality? Drupal 6 Advanced Forum is very capable, but the basic installation doesn't offer many features. For example, by default there is no signature possible.

What modules/plugins/things do you recommend adding to provide a well rounded set of improved functionality in Advanced Forum?

For example, Apache Solr is meant to be a very good add-on to provide improved search functionality. There will surely be lots of other modules that you can think of that would be needed to provide some of the features that come as standard in 3rd party software. Which modules would you say are the most useful ones to have?

Edit:

One need of the forum is to support posting from a mailing list. It can do this already, but maybe there are nice features that can be added to improve this. Perhaps something that makes e-mail formatting look better in a forum, if that is necessary.

Anti-spam is important too. I don't know whether there is a single, catch all anti-spam module. Perhaps there are several modules that should be used here.

The forum is important for community building, so plugins that would help there, for example things that make profiles more informative.

I am interested in all sorts of good functionality. I would like to hear about plugins that people suggest because they are useful, even though I haven't referred to them in this post. That is what I am hoping for. I don't know what to look for / what good things to add.
While I do think this question is off-topic for this site, I know what you're going through. I recently built a forum with drupal, and I was surprised at how difficult it was to choose a good module to fulfill certain requirements, or even how to find the right ones for the job.

So to help you out, here's some modules I used to add functionality to the forum:


Flag + Flag Abuse
Privatemsg
Subscriptions
ACL + Forum Access
Author Pane
AutoAssignRole
CAPTCHA + reCAPTCHA
Comment Permissions
Comment Upload
Custom Search
Flatcomments
Override Node Options
Private Upload
Quote
User stats