Apple's FaceTime app lets you make video or audio calls from your Mac to any of your friends and family for free, as long as they have an iPhone, iPad, iPod touch or Mac.
Using your Mac's built-in FaceTime or iSight camera and built-in microphone, you can talk face to face. If you want, you can optionally use a connected camera and microphone instead.
Alternatively, if you're put off...