Plugins extend WordPress capabilities and there are literally thousands freely available online. That being said, we suggest caution when choosing plugins.
Firstly check the description of the plugin before downloading to see if the creator is updating the plugin regularly and if it is 100% compatible with your WordPress instal version.
Where plugins are concerned less is always better. A huge percentage of WordPress and theme problems stem from incompatible or out of date plugins.
So always ask yourself, can I manage to do without this plugin. If your site has a problem the first place to check is your plugins.
To check; disable the plugins one at a time, and recheck your website. This is the fastest way to eliminate problem plugins.
I am hesitant in recommending any plugins as I do not know what theme you are using and what your particular website is designed to do.
However there are some essential capabilities you should add to your site via plugins, it is up to you to find and test the plugins that will perform the following functions:
Speed up your site: If you care about the speed of your site, Quick Cache [ or similar] is one of those plugins that you absolutely MUST have installed.
BackUpWordPress: Simple automated backups of your WordPress powered website.
Easy Theme and Plugin Upgrades:This plugin allows for installed themes to be upgraded by using the Appearance > Add New Themes > Upload feature of WordPress. Without this plugin, themes can only be installed using this method, requiring you to first delete the theme before installing the newer version. Now features the same easy upgrading for plugins via the Plugins.
Optimize Database after Deleting Revisions: Optimizes the WordPress Database after Cleaning it out.
Really simple Facebook Twitter share buttons:Puts Facebook, Twitter, LinkedIn, Google “+1”, Pinterest and other share buttons of your choice above or below your posts.
WP Show IDs:Simple, yet elegant. Shows IDs for Posts, Pages, Media, Links, Categories, Tags, and Users in the admin tables for easy access. Very lightweight. Also supports Custom Post Types / Taxonomies.
If you are using Google Analytics; Super Simple Google Analytics:Bare bones option for people looking to simply insert the basic Google Analytics tracking code into the head section of every page without any fuss.