IMO - Jillian Michaels - Winning By Losing is short, sweet, to the point. It's a lot of work and sweat - but at least it doesn't lie (no "exercise for 5 minutes a day and you will look like a model"). Plus, you get input from all the chicks already following it.
Check out the
Questions for Jillian thread or the other checking threads in the
Biggest Loser Forum. All I can say is that I actually attempted jogging for the first time since high school...(let's just say it was last millenium.
) and I'm kicking butt (literally - except it's my own) at the gym.