I’ve used Wordpress for about a year and a half now, and I’ve gotten to know the best plugins out there. Here is a list of my favorite twenty (in no particular order):

1 Blog Cacher - A simple caching plugin for Wordpress. I’ve gotten more success out of it than I got out of WP-Cache. (full review)

Akismet - A comment spam blocker. Akismet has caught over 3.5 billion spam comments in total, and about 2 million just today! Akismet is included with Wordpress, all you need is a Wordpress.com API key to activate it. I haven’t gotten many spam comments yet, only 75, but Akismet has made this all so easy because I didn’t have to mark any of those as spam, it detected them all by itself!

InstantUpgrade - A plugin that will upgrade your version of Wordpress to the most recent version (or any other version) with 1-click! If you hate upgrading Wordpress, this plugin is for you. My only suggestion would be for it to put up a maintenance page for the 1-5 minutes that your site is down while upgrading (users get a 403 Forbidden error). (full review)

Subscribe To Comments - When users comment on your blog, do you ever feel like you are responding for no reason? Will they come back and check for new comments on all the posts they comment on? Because of RSS, lots of people don’t visit websites to find new posts, they just wait for the posts to come to their RSS reader, well Subscribe To Comments has a similar concept, but it sends the notification to the users email address, making sure the comment doesn’t go unnoticed (like it would if you had a simple “subscribe to comments via RSS link”, and the user clicked “Mark All as Read” in their reader).

SRG Clean Archives - Using the power of moo.fx, this archive plugin looks fantastic! Take a look at my archive page! You click on a month, and get this super cool effect revealing all the posts for the month selected.

Feedburner FeedSmith - Locates all feed access points and redirects them to your Feedburner feed, where you can add FeedFlares, get some stats, and lots more!

WP 2.3 Related Posts - Shows posts that are related to the current post being read, based on tags. If no tag matches are found, the user will be presented with either the top commented posts, or random posts depending on what the administrator has set.

PodPress - If you are a podcaster, than PodPress is a must! PodPress includes download stats, automatic podcast feed generation, a media player for audio and video files, and lots more!

Gregarious - A social bookmarking plugin that integrates the Share This plugin, the Digg API, and a slick AJAX interface. Gregarious is so easy to setup, it requires no template edits!

Comment Relish - Comment Relish sends an email to visitors who have posted their first comment on your blog, as a little welcoming! This is a great way to get these users to return to your blog.

Wordpress.com Stats - Get blog stats using Wordpress.com’s stats engine. Simply upload the plugin, activate it, grab a Wordpress.com API key, and boom!

Google Sitemaps - Generates a XML sitemap of your blog that is compatible with Ask.com, Google, Yahoo, and MSN Search.

What would Seth Godin Do - Shows a welcome message to first-time visitors, which can be customized to include anything you want. Runs off of cookies, and is not compatible with the 1 Blog Cacher plugin.

BackUpWordpress - Backs up your Wordpress SQL file, and all of the files in your main Wordpress file directory.Backups are a must in the technology world, and not just with your computers hard drive, don’t forget about backing up your blog. (full review)

FireStats - FireStats provides an extensive amount of information about your visitors.

OneClick Installer - If you are a FireFox user, then OneClick is a must have FireFox extension! You simply go to a theme or plugin page, right click and mark it as a theme or a plugin, and OneClick will upload it to your server for you!

404 Notifier - This is a really useful plugin to see how many hits you are getting are 404 hits, what URL they are trying to access. This data is delivered in an RSS feed, or via email.

AJAX Comments - AJAX Comments allows your visitors to comment, but instead of reloading the page to submit and show the comment, why not impress your readers with a little AJAX. AJAX Comments validates, submits, publishes, and reveals comments without reloading the page, your readers will find it quite impressive.

No Self Pings - No Self Pings is a really simple plugin that stops Wordpress from pinging itself. For example, if I like to another post on this blog, Wordpress will ping it, leaving an ugly trackback on that post; that is quite pointless. No Self Pings prevents Wordpress from doing this.

SezWho - SezWho is a distributed reputation system for blogs, forums, wikis, video/picture sites, and any other social media sites. People rates your comments and give you reputation, then others can see other SezWho-powered blogs that you have commented on.

Well, thats about it! Which plugins are your favorites? I love hearing about new plugins!

UPDATE (12.26.07): I’ve found some new plugins I love. Let’s expand this list:

WP Super Cache - I’ve had more success with this great caching plugin than either WP-Cache or 1 Blog Cacher. This plugin is really great, be sure to check it out!

AdServe - A great advertisement management plugin for Wordpress. It rotates lots of advertisements for you. It provides some of the features of OpenAds, but in a very easy to setup environment, and limited features (just enough features!). (full review)