This hack adds a button to the backoffice editing page that lets you display code in a blog post.
This hack counts how many times an article has been read. This is a high performance solution which works quite well. Read forum topic for the implementation.
What this does: it redirects the client (and no server redirect!) to a new URL. Because I renamed my index.php to goedzo.php, this works for the real user. The spammers will never follow this redirect.
This hack cuts the bandwidth spammers steal when they try to hit your blog if they are in your antispam table. Easily installed, and the biggest (first) part can/will survive upgrades.
This hack provides one of the most requested features the forums have ever seen. If you apply this hack and have open registration, then a person can register at your site and have a blog automatically created for them, including permission to post on it. As EdB says, use this at your own risk.