EQ vs. IQ: What makes an effective leader and how can we cultivate these qualities?

I recently attended a workshop on emotional intelligence in the workplace, and it's got me thinking about leadership styles. I've had bosses who ruled with an iron fist and others who took a more collaborative approach.

In your experience, what qualities make for an effective leader? How important is EQ versus IQ? And how can we cultivate these skills in ourselves and others?