Themes

Genesis - Created by StudioPress, this is one of the most popular Wordpress theme frameworks in the world. Price: Free

Search Engine Optimisation

All in One SEO - Makes on-page SEO a breeze by automating a bunch of settings for you, such as hands-free META descriptions. Price: Free

HeadSpace2 SEO - As a simple alternative to the previous plugin, this makes it easy to override the META tags on each post. Price: Free

Affiliate & Revenue

Affiliate Link Cloaking - this plugin makes it easy to obscure your affiliate links, but also more importantly, keep track of the number of clicks you are receiving with nifty dashboard reporting. Price: Free

WP Simple AdSense Insertion - contrary to the name, you can use this plugin for more than just AdSense. Any ad network will work too. Adding banner ads and monetizing your blog is now so easy and requires no HTML knowledge. Price: Free

Security

Limit Login Attempts - this is an essential plugin for every Wordpress website. Bruteforce attacks are common and since Wordpress is the most popular content management system out there, it also makes it the biggest target for attacks. This will help harden your site and reduce the liklihood of a hacking attack. Price: Free

Images

NextGen Gallery - if you want to add a thumbnail gallery to your site, this is the most popular way of doing it. The only downside is that it doesn't use the built-in Media Manager but stores images separately from the rest of the website, which is weird. But it does the job and the price is right. Price: Free

Responsive Lightbox - if you're looking for a pop-up effect on your indivdual images, this plugin will do the job. Very flexible and the learning curve is small. Price: Free

Management

ManageWP - when you have multiple Wordpress blogs you'll want a central control panel to modify and manage them. This invaluable tool also allows you to easily setup a new Wordpress blog by duplicating an existing one you have. A real timesaver when you're building your blog empire. Price: Free Trial

Google Analytics for Wordpress - adding the tracking code into your Wordpress blog now requires no code edits. Perfect for a newbie who doesn't want to get his hands dirty. Price: Free 

Miscellaneous

Exclude Pages - this is one of those features that should just be in the core of Wordpress. When you create a "privacy" or "terms of use" page you do not want it showing up in the top navigation menu. So this adds a simple checkbox to hide specific pages. Easy. Price: Free

WYSIWYG Widgets - If you want to customise the sidebar in your blog with super flexible images and/or text, this does the job simply and effectively. Price: Free

WP Engine - If you're serious about growing your Wordpress blog, check out WP Engine for managed hosting. They take care of all the nuts and bolts so you can focus on growing your business. Price: from $35/mo