I have chosen these three addons because they seem compatible with Windows Visual Studio 2011, therefore can be potentially used for one of the upcoming projects.
ofxRemoteUI
Description: this addon allows you to remotely modify the properties of your variables. It uses the client/server model to establish the connection between two programs that could be installed on different devices.
Significance: this addon may be helpful for remotely manipulating volume or luminosity for instance, or control animated visualizations from multiple devices.
ofxMidi
Description: ofxMidi enables developers to add a musical digital interface to their projects.
Significance: adding sound to projects always makes them more fun and desirable.
ofxUI
Description: this addon helps developers create and customize user interfaces. UI elements include buttons, dropdown menus, labels, sliders and so forth.
Significance: ofxUI can help developers focus on the functionality of their features rather than their visual rendering.