Basecamp: This project and task management app is beneficial if you work on your own and is even more powerful when you have a team (like a virtual assistant), so that everyone can see the status. (NOTE: Requires a subscription.)
DocuSign: Who needs hardcopies and fax machines when you can have your clients sign documents electronically? You will even receive automatic confirmation when the other party has signed.
Dropbox: Allows you to sync documents across all of your devices and access them anywhere. It also allows you to share files with clients by giving them access to only the files you want to share.
Evernote: Take notes any and everywhere, and store them in a multitude of formats including text, voice, photos, and webpages.
Skype: Have face-to-face meetings without leaving your office. Skype saves time and expense--you can speak with anyone in the world for free!
I discuss the importance of maximizing technology in my Udemy course: Productivity & Time Management: Grow Your Side Business. For more information about the course, click here. The video that accompanies this blog post is a clip from the course.