I've released the new WordPress plugin Simple Trackback Validation.
How it works:
When a trackback is received, the plugin retrieves the web page located at the URL included in the trackback. If the page contains a link to your blog, the trackback is approved. But if the page does not link to your blog, the trackback is placed into the comment moderation queue (or optionally marked as spam).
It is similar to the known plugin "Trackback Validator" of Rice University, however it is completely re-coded and has many advantages in comparison to the Trackback Validator, for details visit the plugin's homepage.