My Recommended WordPress Plugins
One of the best parts of working in open-source and especially with projects like WordPress is the community. The community around WordPress is what drives the software forward and makes being a developer easier every day. Developers create themes and plugins and other software that they release as open-source and we all grow and share in our collective ability to develop great things with the help of those in our industry. Just the other day I posted on a forum asking for help with something I'm not very good at(writing SQL) and got a response almost immediately. In a day, a couple of strangers had helped me with my problem and the code they wrote is being integrated into a larger and very popular WordPress plugin. We're not all perfect plugin developers though. Sometimes bad code gets written and sometimes more than one person or team writes a similar plugin and the two face off. I like to keep a list of my recommended WordPress plugins to make starting new sites easier and to have a decent codebase for reference. Here is where I'll try to keep an updated list of the plugins that really make me happy.
Adrotate - This is like Google's Doubleclick for Publishers but integrated into your WordPress dashboard and it doesn't require you to use iframes or a third party service. It's really well made and pretty easy to use. It also has a very comprehensive list of ways to control and track your advertisements and advertisers. I made a small contribution to this one so you should definitely get it ;)
Akismet - It comes with your WordPress install but it's not just a cheap add-on to be thrown in. This is seriously good and helpful software. If you're not running Akismet, you'll quickly find that your comments are 90% or more spam. Install it, run it, never worry about spam ever again.
bbPress - The best and easiest to use forum plugin for WordPress. Just activate it and you're set to create a new forum. Easy to configure permalink structures, integration with Akismet to prevent spammers from posting all over... Highly recommended WordPress plugin.
Cart66 - An e-commerce plugin. It adds a store management section where you can take care of all your products, inventory, orders, etc and then you add those to posts or pages using their convenient shortcuts. Really useful if you don't have a ton of products or want to add a "buy now" button in non-traditional places like the middle of an article. Best part here is the very easy to use integration with other e-commerce and related APIs like paypal, spreedly and fedex.
CodePress Admin Columns - I started coding something similar to this plugin but stopped when I found it. It's a brilliantly easy way to add extra informational columns to your post listings. It comes with a litany of options for what columns to add and takes care of the details smoothly. I strongly recommend this plugin if you need extra info like the post thumbnail in your post listings.
Contact Form 7 - The most popular contact form software for WordPress. Woofoo is also really great but it costs money so I tend to avoid it. Easy to install, easy to make forms, it even has a file uploader with options for restricting the file size and type. Really useful!
Developer - One of my favorite plugins. It's a plugin made for developers. It provides an easy interface for configuring your site development environment. Like installing a list of common development plugins from a single window.
Duplicator - My favorite plugin for migrating your WordPress site from one host to another. It makes an exact copy of your install and copies your entire database and makes them available for download with a PHP script that will put all that data in the right place on your new host. It's a little rough cut as it requires a bit of know-how to install on the other end and it doesn't have the prettiest interface but it's definitely the most exacting way I've found to move sites.
Force Strong Passwords - The name pretty much says it all. It requires that your users sign up with strong passwords. It's quick, simple and performs a very much needed function. I recommend everyone install this plugin on every site.
JetPack - This is one of the most useful, most powerful plugins out there and a must-use for all my sites. JetPack brings a lot to the table with traffic stats, infinite scroll, mobile theme, automatic publishing to your favorite social sites... It's got a ton of functionality and I strongly recommend you use it in all your sites if you're not already doing so.
Limit Login Attempts - This plugin provides a simple way to restrict people from brute-force guessing passwords on your site. If somebody gets a password wrong too many times their IP is blocked for whatever amount of time you specify. It can even send you emails to let you know when someone has been blocked. Super useful for security.
Love It - Written by Pippin Williamson, this simple but elegant plugin provides a way to allow your users to "like" things as they do on facebook or other social sites. It's well-coded and runs on AJAX so the page doesn't refresh when the love-ing button is clicked. Great plugin by one of the best WordPress developers out there.
Mailchimp List Subscribe Form - If you use Mailchimp, odds are you've created a form or twenty to embed somewhere. This cute little extension allows you to embed a Mailchimp form anywhere on your site using WordPress code. The user's information is submitted via AJAX and provides instant feedback.
Multiple Post Thumbnails - This is the kind of plugin I really enjoy. It does one thing and it does it well. This adds an interface to WordPress to have more than one "featured image" so you can do things like have your featured image change when it's hovered over or put one at the top of an article and two more at the bottom. Whatever you like. Very useful.
Post Author Box - Great way to promote your authors and improve your company's social presence and conversion rates. This plugin allows you to add a customized blurb about the author at the end of the post. I strongly recommend this for news and related sites.
S2Member - If you need a way to add different levels of membership to your site, I strongly recommend this plugin. It allows you to create different kinds and levels of membership and restrict different parts of your site to just the members you see fit. There are a lot of membership plugins out there and most of them don't work that well. This one does exactly what it's supposed to. Get it.
WP Click Tracker - If you're looking to enhance your users' experience by figuring out what they use your site for, this is a great, non-intrusive way to do so. Tracks every link in your articles that your users click and even provides some really nice charts to show you what time of the day they're most active, what days of the week and clicks over time. Great to see what your users are interested in through a different lens than just pageviews.
WP-Invoice - This is a life-saving plugin for me. It creates a simple way to manage billing from your WordPress dashboard. Create invoices, send them, offer invoices, receipts and payment all in one place on your site. For the freelancer this is easily the best way to keep track of invoicing clients and when you get paid. One of my most recommended WordPress plugins.
WP-Polls - Great plugin to run polls on your WordPress site. It's simple and effective and well written. It's also recommended by some of the top names in the industry. Another great way to get to know your users better too!
WP User Frontend - Allows your users to log in on the frontend of the site and restricts access to the WordPress dashboard. Really useful if you're running a site that requires membership.
Yet Another Related Posts Plugin - By far the best plugin for displaying related posts/pages to your users. It's elegant, useful and very popular. A small caveat is that it runs full-text searches on the articles in your database which can significantly slow down your site/server under heavy traffic. If you get a lot of traffic, I'd recommend a custom solution or using a service like nRelate which provides similar functionality and still free.
I also have a seriously ridiculous unorganized folder of plugins and sample scripts that I'm a little bit afraid to go into. If you're looking for a plugin with specific functionality that isn't here, feel free to contact me and I'll do my best to help you out.
UPDATE: WordPress.org now has a feature where you can "favorite" plugins on the site and even bring up those favorites when you're installing plugins via the WordPress dashboard. A current list of my favorite plugins there and what I've been up to in the community can be found here: http://profiles.wordpress.org/jacopovip