There are several thousands of WordPress plugins in the WordPress community and new plugins are coming out everyday. However, not all plugins are useful, in fact some are very bad written that will mess up your site or harm your WordPress installation. So how do you know which plugins are right for you? Well, here is a list of plugins that I have used or played around before. Hopefully you will something useful here.
To save your SQL server resources, WP Cache works by caching Worpress pages and storing them in a static file for serving future requests directly from the file rather than loading and compiling the whole PHP code and then building the page from the database. It is a very useful plugin if you have a high traffic site or low performance server.
Want to sell stuffs on your blog? You must check out this WP eCommerce plugin by Instinct. It is an Ajax powered shopping cart, very easy to use. You can setup your shop in minutes through the Admin panels.
I've been using this contact form for over a year. It works very good and filters all the spams. Seriously, NO SPAM at all. It also allows you to customize the email subject, thank you messages, and adds addition form fields.
One of the popular WordPress plugins, Sideblog is the best way to post short notes on the sidebar. I use it for Best Web Gallery. It gives you options to define the sideblog category, how many entries to display, and whether to exclude from RSS feeds.
WP PageNavi adds a better paging navigation to your WordPress site. It is nice if you have a lot of posts because it allows your visitors to skip from page to page. I use it on N.Design Studio and Best Web Gallery.
Sociable appends a list of the social bookmarking sites (ie. Digg, Del.icio.us, Reddit) at the end of your posts and allows your visitors to bookmark. I used this plugin before and it worked very well.
WP Post Ratings adds a 5-star Ajax rating system to your posts/pages. It works like a charm. Hint: most CSS gallery sites use this plugin.
A very simple yet effect Ajax comment plugin, it checks if all fields filled correctly (so your visitors will never see the default error messages), and also makes sure to avoid comment duplication, and has flood protection capabilities as well.
This plugin gives your visitors an Ajax live comment preview. It is great if they need to enter HTML tags in your comments. So, no more syntax errors in your comments.
As seen on Web Designer Wall, it adds a Ajax poll system to your site. It is very flexible with a lot of features. Layout is completely customizable via Admin panels. It also allows you to archive the polls. Highly recommended!
It basically display a Gravatar (globally recognized avatar) of your commenters. In case you don't know yet, Automattic (WordPress creator) just acquired Gravatar and the future Gravatar services will run faster and bigger sizes (up to 128px).
Digg this is a WordPress plugin that detects incoming links from Digg.com to your wordpress post and automatically display a link back to the digg post, for people to digg your story. When a digg is first recognized, it will send an email to the site’s admin.
Subscribe to Comments 2.1 is a plugin that allows commenters on your blog to check a box before commenting and get e-mail notification of further comments. You probably seen it already, it adds a checkbox "Notify me of followup comments via e-mail" in the comment form.
I've been this plugin since my first WordPress site, it is a must have for every WordPress site. It saves me so much time and clicks. It basically makes your secondary menu activate on mouseover. For example, instead of click Write, then click Page; you can mouseover Write and click Page (this will save one click and one pageload). Big time saver!
Adsense Deluxe is probably the best Adsense plugin available on the web. Very easy to use: first you define your ad code through the Admin options, then insert a HTML snippet ("<!–adsense–>") into anywhere of your post content, and it will automatically repace it with your ad code.
Default WordPress search engine doesn't search metadatas, static Pages, etc. This plugin allows you to search everything in the database. Of course, it comes with options, so you can set what to search.
If you use calendar in your sidebar, consider this Ajax Calendar. Your visitor can browse through the calendar without refreshing the page.
Although not many sites use breadcrumb navigation now, but if you want, here is one: Breadcrumb Navigation XT. It basically lets you add a breabcrumb navigation to your site.
If you need to generate a XML compliant sitemap for search engines, Google Sitemap Generator is the best choice (supported by most popular search engines: Google, Yahoo, Ask.com, and MSN).
Another must have plugin. In fact, it is in all my WordPress sites. It outputs a list of recent comment excerpt. You can install as WordPress plugin or simply include in your theme folder (no activation required). Simple!
As of version 2.3, WordPress has a built-in tagging system, however with very limited features. Simple Tags gives you more features: type-ahead / auto suggestion tags, manage tags (rename, delete, add..), edit mass tags, dynamic tag cloud colors, and more!
Not sure if anyone would still signup newsletter since we have RSS now. But newsletter is the best way to inform your subscribers with new products and updates. I find this plugin will be useful if you run a WP eCommerce shop. It is not free (cost $14.99), but totally worth it (check out their features).
This plugin is useful if you get a lot of comments on your blog. It breaks your comments into a number of pages. Imagine if your blog gets over a thousand of comments? You definitely need this plugin.
This plugin allows you to easily display Flickr photos on your weblog. It supports user, public and group photostreams. The plugin is relatively easy to setup and configure via an options panel. It also has support for an image cache located on your server.
Theme Switcher allows your readers to switch among installed themes. This plugin is useful if you offer WordPress theme and you want to let your users to preview the themes. I use it to showcase my free WordPress themes (demo here).
If you still think these are not enough, you can digg more at: