How would you like the ability to display related entries on a 404 page? It would be really handy.
This plugin displays related posts depending on which page tried to be accessed, and it does so by attempting to match the keywords in the requested URL – basically the post slug – with the keywords from other post slugs.
You might need to tweak your Permalink structure to make it work.
I have a really neat idea for a plugin that will actually take into account tags and even keywords from other posts when displaying related ones so it’s not relying on a certain Permalink structure to work. Let me know if you’re interested, and I might squeeze it in one of these days.