1. DiggThis – This plugin was written by Aviran Mordod This by far my favorite DiggThis plugin because it only displays on posts which have been submitted to Digg. My opinion, which is shared by many others is that, it’s better to show a DiggThis button when the article has been submitted to Digg rather than showing a Digg button next to every article. Unless you are ReadWriteWeb or some other mainstream blog, those buttons will show 0 diggs and will possibly hint to the content not being up to snuff. I suppose its one of those psychological things.
2. Highlight Author Comments – This plugin written by Rob Marsh, SJ. makes following comments written by the blog author a cinch. After installing and then activating the plugin, you can style what blog authors comments will look like, giving you the ability to distinguish your comments versus all other comments.
3. No Self Pings – No one has been able to tell me what the purpose is behind WordPress sending pings and tackbacks to itself if you link to an article located in your archive. I’ve found myself always deleting these pingbacks. Thanks this this plugin written by Michael D. Adams. this is no longer an issue for me. Now, I can easily link to myself without having to deal with those pingbacks giving me that much more free time to do other things.

These are three plugins which I feel are under rated that I use on my own blog. I invite you to partake in this meme and highlight three plugins you are using on your own blog that you feel are under rated.