A very successful system most people don't know about is betting on a coach (whether it's a head coach or coordinator) going against his former team.
If you just look at some examples from 2007, you'll see that this works. The Cardinals pulled a huge upset over the Steelers because of Ken Whisenhunt and Russ Grimm. The Giants swept Philadelphia because Steve Spagnuolo used to be on the Eagles' coaching staff. The Lions crushed the playoff-bound Buccaneers because of Rod Marinelli's familiarity with his former squad.
Of course, nothing is guaranteed to work at a 100-percent clip, but playing this system will reward your bank account handsomely.
Here are all the head coaches and coordinators who worked with other teams recently. Keep in mind some coaches aren't listed for former teams if there have been major personnel changes (i.e. Dick Jauron wouldn't work for the Lions anymore).