My favorite kickboxing workout of all time is Cathe's Kick, Punch, & Crunch. I also really enjoy Kick Max and Cardio Kicks.
Some others to try are Tracey Staehle's Cardio Sweatfest (contains a 60 min kb workout and a 30 min hi/lo workout) and the Powerstrike workouts. If Cathe's intensity is 8-10, I'd put Tracey's workout at about a 7 or 8. It's fun.
Powerstrike 1 and 2 are pretty comparable in intensity to Cathe's intensity, just a wee bit lower. They are low impact, too. They are only available on VHS. Powerstrike 3 is less intense, but it is available on DVD (I'd compare this one's intensity to the first part of Kick Max,). I don't have Powerstrike 4 so I can't comment on that one.
I've heard good things about Kimberly Spreen, but I haven't tried any of her workouts.
HTH