Well, I have over 100 videos and DVD's, so I definitely do more than Cathe, especially for cardio! I need the variety also...and I think it's a very healthy way to go.
For me, a mixture of Cathe's strength tapes with cardio from other instructors (I can't take the torque and speed in most Cathe step tapes) is a great combination.
After being on a Cathe strength "binge" for several months, I decided to mix it up and alternate Cathe with the Firm. I find that it's a great combo. Something about the Firms use of step ups and hover squats, or SOMETHING, really worked the low end of my squats, and I went back to Cathe being able to lift with more ROM on my squats.
It's hard to give general recommendations, because I don't know if you like dancy (I don't) or if you're looking for cardio or strength or what.
I really like the Firms new Sculpting System, but for the moment, it is only available as a 3 video/DVD set and you have to buy a "sculpting stick" with it.
For kickboxing, I recommend Powerstrike...led by two women with great form. It's a non-dancy, drill-like workout.
Other good instructors are Gin Miller (though she hasn't done much new in Step for a while, there are some "instructor" tapes on her site that are do=along workouts). She does some interesting work with functional strength and stability ball workouts. Her videos are available at ginmiller.com
Mindy Mylrea is someone a lot of advanced exercisers like, but I find her too fast for me. She does very athletic cardio and functional weight training.
I'd recommend visiting videofitness.com and checking out some of the reviews in areas you're interested in.