Well, my first proper one, anyway
Only a few days after I finished my PHP day of birth script, I wrote my first proper MyBB plugin. My first plugin was a Return to Top postbit button, but I'm not really counting that :P This plugin will add a message to the index of your forums if a member is awaiting activation, and you have account activation set to either email or admin activation. You can choose to turn the message on or off, specify a different title for the email/admin message, and a different message for the email/admin message. The message will display in your theme's style and is collapsible. I've wanted this for a bit but really wanted to do it myself, so once I'd furthered my understanding of the basics, I tried, and got it finished quite quickly. I had to look at how some other plugins were made, mainly to see how to setup the settings, and how to make the template changes. Anyways, I managed to create it quickly and with hardly any problems. It's now been downloaded a few times already and I've had good comments back, which is great. It was a good first plugin idea, and it turned out even better than I planned. It's available for download from the MyBB Mods site, where you can also see screenshots, and the discussion thread can be found here. I already have another idea for a plugin, which may be ready in a week or so, once I have time to get it right.