I've been running a consultancy for a little over 8 years and in that time I've discovered several extensions and tools that are not only the right tools for the job, but must-have solutions for running a Joomla focused business.
If I were to start fresh today as a bootstrapper, freelancer, consultancy, or online business using Joomla, this would be my shopping list.
Your Joomla website is your 24/7 salesperson, your 3:00 AM customer service representative, and one of your core channels for bringing in new business. I consider these extensions a core need for almost every Joomla based business.
Chances are slim that you do not already have this extension installed, but if you don't Akeeba Backup is the very first extension you should install on your Joomla site. Period. I recommend opting for the professional version and setting up automated backups to an off-site resource (We use Amazon S3, but Dropbox is easy.) Even if your web host says they provide you backups, you should still maintain your own for redundancy and to make sure that you have the most options for when disaster strikes... Because it will.
I've been writing on security quite a bit lately, and for good reason, hackers are more aggressive than ever. An application firewall is a strong line of defense against having your site compromised (though it doesn't replace staying up-to-date and following good security practices.) We use Admin Tools Pro for the most part, but I've been impressed with RS Firewall as well.
RS Forms Pro
Having your Joomla site as an always available representative of your business is powerful, but many sites only provide one means of communication: from you to your customer. Forms enable you to open up communication from them to you. At their most basic, you have a simple contact form, but using an extension like RS Forms Pro enables you to easily streamline your interactions by creating more complex forms to collect relevant information in advance of the phone call or email to follow.
Even if you have no intention of blogging regularly, having a blog on your site is a powerful addition. Every business needs a soapbox and a blog is an ideal platform to stand on when you need to communicate with your customers, leads, and clients. If you do decide to blog regularly it is a powerful tool for developing your brand and building the website as a channel. Easy Blog is a polished solution which has advantages over normal articles in commenting and social integration.
JCE is a powerful little editor which we particularly like because of the image management features. (Pro Tip: Edit the plugin options down to only what you actually use. The simplicity makes it much quicker to find what you need when you need it.)
Joomla Has Come a Long Way
I thought quite a bit about additional Joomla extensions to add to this list, but these days the Joomla core is pretty powerful. When I first started developing for 1.5, the Joomla extensions list would have been probably twice as long to cover things like search engine friendly features, ACL, content organization (subcategories and tags), module placement, and more. Now, when we do an installation, we're almost only installing extensions that make the site behave in a unique way. As a comparison, I set up a WordPress blog recently and was blown away that you had install a plug-in to manage meta-descriptions. To me, that's something that should have been added 5 years ago (especially for a blogging platform.) So if this list seems a little Joomla extension light, consider that it speaks well of the core developers and the people that have contributed to the project over the years.
Think something is missing? An essential extension for every site you build? Add it to the comments below and say why so that others know what makes it great.