Here at New Media Campaigns, we build client sites on a variety of Content Management Systems including Drupal, Craft, Wordpress, and our very own HiFi. WordPress makes up a fairly large percentage of our work, due in large part to its ease of use for content entry, clients' familiarity with the system, and its extensibility through Plugins.
Plugins extend and expand the functionality of core WordPress; there are currently more than 47,000 listed on WordPress.org. They're typically developed by independent firms or developers and also maintained by that group. The open field presents both pros and cons. The pros center on the fact that you're able to leverage the collective wisdom and work of others to more quickly build a powerful site through functionality that has already been developed and proven. The cons relate to the fact that some plugins in the ecosystem can fall out of date, causing security issues, or they simply just don't work as advertised. When working with plugins, it's important to make sure they're up to date, have good base number of installs and review, and are being actively improved and secured.
Through our dozens of WordPress projects, we've come to consider a group of plugins nearly essential for each project. Below is a list of our favorite plugins. Feel free to add to the list in the comments!
Advanced Custom Fields Pro - ACF Pro is probably the most powerful plugin in our toolbox. ACF allows for the easy and manageable creation of custom content and flexible layouts. The flexible layout tool alone would be worth installing this plugin, but you can rely on it for just about any custom content scenario you can imagine. The plugin author and maintainer, Eliot Condon, is responsive and manages a vibrant support forum. The developer license is well worth the one-time $100 price tag.
Timber - We use Twig (http://twig.sensiolabs.org/) for most of our templating across all of our CMS installations. Timber brings Twig to WordPress and it is vital to our development process. Not only does Timber allow us to use a templating engine with which we are extensively familiar, it brings sanity and order to the WordPress templating system allowing for the separation of PHP and HTML code. This separation makes for much cleaner and sustainable code overall which in turn makes the site more stable and easier to maintain and extend. Upstatement’s Timber documentation is helpful, illustrative and backed by a responsive forum addressing all sorts of complex interactions with other powerful plugins like ACF Pro. Timber is free and open source.
Formidable - Besides having perhaps the coolest plugin name around, Formidable is a rock solid form plugin. Out of the box, it has great layout options, form field choices and ajax form submission. The pro version is very reasonably priced and unlocks a ton of useful features like conditional logic, multi-page forms and a visual form styler. Also available are a suite of add-ons enabling integration with third-party services like PayPal and Mailchimp.
Yoast SEO - SEO setup can be a time-consuming hassle. Yoast SEO handles all the important areas like post titles and meta descriptions, permalink cleanup, XML sitemaps, robots meta configuration and RSS enhancements while also offering tips on readability. You can access your Google Analytics dashboard from within the plugin making it a one-stop SEO management portal.
Relevanssi - WordPress search is somewhat lacking. Relevanssi offers all sorts of customization options like term weighting, stop words, “did you mean” suggestions, highlighting, and fuzzy matching. The index is automatically updated when new content is added and user queries are logged so you can continue to improve results over time.
Post Types Order - We build a lot of custom content types and this simple-sounding plugin keeps everything sorted. A new ordering screen appears near all content types and a drag-and-drop interface gets the job done.
This list is by no means comprehensive of all the plugins we use, but just the ones we find ourselves going back to again and again. Add your favorites to the comments, and we can add them to the list!