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.

Want a random quote plugin ? Want to change the old boring comment pages full of “Joe said” with something random like “Joe thought”, “Joe wrote” and “Joe replied” ?
Random Words is a WordPress Plugin allowing you to manage a number of lists with any items, and display random items from these lists. Everything is managed from within the Admin interface of your blog, in a very neat interface.
For documentation and tips, please refer to the official plugin page for <a href="http://planetozh.com/blog/my-projects/wordpress-plugin-random-words/" title="Random Words" rel="nofollow ugc">Random Words</a>

Ozh' Random Words

Create list of items and display random item. Random quotes, or replace "Joe said" with "Joe said/commented/wrote/thought"...

Ozh' Auto Moderate Comments vs Ozh' Random Words