When a post gets old, instead of simply closing the discussion, send comments and trackbacks to the moderation queue. This will greatly reduce spam.
For documentation and tips, please refer to the official plugin page for <a href="http://planetozh.com/blog/archives/2005/02/02/wordpress-plugin-auto-moderate-comments/" title="Auto Moderate Comments" rel="nofollow ugc">Auto Moderate Comments</a>

Ozh' Auto Moderate Comments

When a post gets old, instead of simply closing the discussion, send comments and trackbacks to the moderation queue.

Boone Gorges

<a href="http://yourls.org/" title="Your Own URL Shortener" rel="nofollow ugc">YOURLS</a> is a free URL shortener service you can run on your webhost to have your own personal Bitly.
This plugin is a bridge between <a href="http://yourls.org/" title="Your Own URL Shortener" rel="nofollow ugc">YOURLS</a> and your blog: when you’ll submit a new post or page, your blog will tap into YOURLS to generate a short URL for it.
This plugin also features BuddyPress support. Short URLs can be generated automatically for each member and each group, and are customizable if permitted by the BuddyPress administrator.
Requires PHP 5.
Note: this plugin should still work but is no longer maintained. See http://yourls.org/#More#wordpress

YOURLS: WordPress to Twitter

Use YOURLS (a free GPL URL shortener service) to create short URLs of your posts, or for your BuddyPress groups and users

Ozh' Auto Moderate Comments vs YOURLS: WordPress to Twitter