RE: Interval Max 4-Ever!
I second the earlier response re Interval Max - I do believe it is the highest-intensity step tape on the market. Lots of truly plyometric intervals, not just rebounding off the balls of the feet and recruiting mostly calves, but half-time vertical jumps, half-time plyo-jacks, box jumps, half-time side-to-side slalom jumps, half-time plyo lunges ("Power Scissors"), airborne jacks and high tuck-jumps, etc. that recruit the quads, hamstrings and glutes for real power. Simple choreography, maximum work and benefits. It's a staple of my home routine.
Also, you may want to check out Reebok / Gin Miller's "Intense Moves" step tape - this is also based on interval training, and includes higher-intensity plyometric segments. It is less intense than I-Max, but higher intensity than most.
Good luck!
Annette