With over 22,000 WordPress plugins in their Plugin Directory, writing a top 10 list is dangerous. After all, what standards should we use? Most downloads? Highest ratings?

Plugins all add different features so it's hard to compare them objectively. For some projects one feature may be more important than another. Sometimes a specific feature may not even be wanted or needed on a project.
Therefore this list is simply the plugins that I like personally and found to be the most useful in my client projects over the last year. That leaves tons of room for debate. So if your favorite plugin isn't in this list, leave a comment. Make your case why I should have included it.
Some of these plugins are pretty popular and you'll be familiar with them. There may be one or two that are new to you. Most are freely available in the Plugin Directory. But I'm including a couple premium only plugins too.
WordPress SEO
Since we're at Search Engine journal it makes sense to talk SEO first. When it comes to that, Yoast's WordPress SEO is my go-to plugin. And I mean no disrespect to the more popular All In On SEO Pack. Michael Torbert and his team are great folks.
But WordPess SEO does more and makes it easier to manage all SEO related stuff with one plugin. This plugin has the usual settings for title tags, meta information and robots.txt commands, etc. Over and above that, the plugin has

• Keyword Research
• Google Snippet Preview
• On Page SEO Analysis
• Webmaster Tools Verification
• XML Sitemaps
• RSS Optimization
• Breadcrumbs
• Social Integration
• Checkbox Removal ofLinks
• Some .htaccess Settings

It's an incredibly powerful plugin. Used properly it will maximize the potential search engine exposure of your content.
W3 Total Cache
Speaking of incredibly powerful, W3 Total Cache is a great plugin for increasing the performance of your WordPress site. When we talk about performance in this case we're talking about making your website load more quickly for your site visitors. Please know that this is a case of "with great power comes great complexity." With all of the things this plugin can do, and the wide array of possible server configurations, W3 Total Cache can be a bear to configure.
For example, here are some of the things this plugin can be configured to do.

• Seamless content delivery network (CDN) integration with WordPress for media and theme files
• Post and Page caching
• CSS and Javascript caching
• RSS Feed caching
• Caching of search results pages
• Database caching
• Minification of HTML, Javascript, & CSS for posts, pages and RSS Feeds
• Browser cache control
• Import media files to your CDN

A faster loading website has SEO considerations because page speed is a factor in Google's algorithm. Higher website performance has also been linked to increased revenue for eCommerce sites as well.
The plus side can be well worth the effort to configure the plugin for your site.
Defensio
Spam is the scourge of the internet. Everybody knows about Akismet for dealing with spam. But if you're just starting out with your business the low $5 a month Akismet charges is noticeable. Fortunately there's a fantastic alternative in Defensio.
I was a beta tester for the plugin back in 2007 when their service was first coming online and it's a solid choice for protecting your site from spam. They have a profanity filter. You can choose to block URL's based on their category. And there it can protect your Facebook profile or page as well.
Their pricing has a free entry level for small businesses under 5 employees or up to 25,000 posts per month. So if you're still getting your business bearings then Defensio is a good option to consider.
Cookies for Comments
Speaking of spam protection, Cookies for Comments is an amazing little plugin that can stop machine generated spam comments even before they hit your server.
When I installed this plugin and added the two recommended lines to the .htaccess file  on one of my higher traffic sites my spam comments went from a couple thousand a day down to about 5 a month. Seriously. It made that much of a difference.
Normally I shy away from plugins that don't list compatibility with the current version of WordPress. But I'll make an exception for this one. Hopefully the plugin developer will update the compatibility as WordPress 3.5 comes online.
Bonus: If you're getting hit with tons of trackback spam check out Simple Trackback Validation with Topsy Blocker. It deals with the other side of the autogenerated spam issue.
The Events Calendar
I work with a lot of businesses, nonprofits and churches that need to have a way to let visitors know when they are holding events. I've found The Events Calendar to be one of the best solutions.
The plugin creates a custom post type for your events and gives you a ton of ways to manage and display your events. The plugin integrates with Google Maps so people can find your location. You can display your events in either a month or list view and there's even a widget you can use to display your events.
If you do a lot of recurring events or your events need custom attributes it might be worth getting the Pro version from the good folks at Modern Tribe.
Digg Digg
There are so many social sharing plugins out there that it can be overwhelming for some one new to choose a good option. Digg Digg was the top of the heap for a at one point, and then went through a season where it was all but abandoned.
The folks at Buffer took over development of the plugin a year or so ago. After watching them for a while I decided they looked to be around for a while so I started using the plugin again.
Digg Digg has a couple dozen of the most popular social media buttons to choose from. You can configure the buttons to display either above your content or below it. Or it can do a floating bar beside your content.
Unfortunately it looks like Digg Digg may be in danger of being abandoned once again. Hopefully not, but if it is I don't see it making next year's top 10 list.
Gravity Forms
There are some solid plugins for creating web forms out there. There's even a basic contact form bundled into Jetpack. So it may seem strange to choose this type of plugin for the first premium plugin in this list. But I find Gravity Forms that good.
I admit I held off buying Gravity Forms for a long time. When I finally did it was a breath of fresh air. All the compromises that I had to make with other plugins disappeared when I started using Gravity Forms.
You can build very complex multi-page forms, forms that show fields based on specific responses. You can create order forms and take payments directly from your website with one of the many addons available. And there are many addons to integrate the plugin with various email autoresponders.
Tip: If you use Gravity Forms be sure to search the WordPress Plugin Directory for free addons as well. There are a bunch in there.
NextGen Gallery
When it comes to managing lots of images on your WordPress site, NextGen Gallery is the gold standard. I've worked with big sites that have tens of thousands of images and this plugin doesn't miss a beat.
You can upload your gallery images via the WordPress dashboard, or via FTP. If you choose FTP NextGen will import them in so that you can easily manage them from the dashboard. If you are a photographer, NextGen will allow you to watermark your images to protect them from copyright infringement.
NextGen is another one of those plugins that has many add on extension plugins available. If you are looking for a complex image gallery solution then NextGen is what you'll want to use.
nRelate Related Content
A great way to keep people on your website is to show them other content they might be interested in when they get to the bottom of a post. Images are often best to entice visitors to click through to another post. There are several plugins that can do this for you. The one I like best is nRelate. Here are some of the reasons why.

• It is Multisite compatible
• It can be used without creating a user account – if folks want to advertise they can create their own accounts
• Their servers do the heavy lifting for determining related posts
• You can designate featured images – but if you don't the plugin will pull the first image from the post
• You can opt for text only links
• You have several different style options for the thumbnail display

Soliloquy
Another plugin type where we have lots of choices is image rotators or sliders. And yes, I'm going with a premium only plugin here too. Soliloquy is a cut above all the other slider plugins I've used over the years. Here are some of the reasons this plugin is worth the investment.
Mobile Responsive – Mobile is where the web is going. You want your image rotators to scale down with the rest of your website.
SEO Friendly – Each image can have it's own alt and title tags.
It's Light Weight – It only loads the required javascript files on pages with sliders. Many plugins load the scripts on all pages of your site.
Multiple Sliders – Soliloquy supports multiple sliders on the same page.
Videos – You can mix and match videos with still images in your sliders.
It's been a bit over 6 months since Thomas Griffin first released Soliloquy. He's working hard to advance it quickly. As a result I think it's the best slider plugin available right now.