Writing Compelling Characters

Let's face it, your story really is nothing without characters that grab the readers by the throat and won't let them go.  Yes, story is iportant, local too, but the characters who populate your stories are what breathe life into it. They're what really draw readers in make them want to know what happens next.

So, that established, how does one create compelling characters?  Characters that leap off the page, then draw the readers down into their own little hell or lift them up to heights...