A friend of mine gave me Cardio Toolbox for a X-mas present (aside: THANKS, JO-JO!!!!!), and IMHO it's okay intensity-wise but if you've cut your teeth on the I'Maxes and Body Max anything other than Cathe won't satisfy very much.
I would like to suggest:
Circuit Max / Cardio Kicks DVD
Cross Train Express (CTX) DVDs
The Terminator DVD (especially for its Gauntlet workout)
The MIC workout (it's on the same DVD as Rhythmic Step)
High Step Training Advanced
Kick Max
Circuit Max has some absolutely top-notch cardio with 2 hi/lo segments, one floor kickbox segment, one step-kickbox segment and two traditional step segments. The six weighted resistance cycles incorporate light dumbbells and compound upper / lower body sets for 2 minutes each; HOWEVER, you can modify that to a serious cardio-leg burn by substituting barbell squats, plie squats and lunges rather than compound upper/lower body stuff. You can even polish that Circuit max variation off with the power drills sequence of Cardio Kicks.
Cross Train Express (CTX) also has good hi/lo (especially in 10-10-10), step-circuit (Power Circuit workout), interval step (Step & Intervals, although the interval segment is only 10 minutes) and traditional step and kickbox. The DVD is organized such that you can do a lot of mixing and matching among cardio segments for a harder and/or longer burn.
The Terminator compilation DVD has Gauntlet, which is an amazing mish-mosh of I-Max 2, Boot Camp and Cardio+Weights. It too is chaptered such that you can do some discrete chapter-skipping past some of the resistance cycles and power through the cardio stuff; the blend of I-Max 2 intervals and Boot Camp intervals are awesome.
MIC has about 35 minutes of hi/lo; the last 15 minutes of this hi/lo is really top-drawer HIGH - high impact, high intensity.
HSTA has a good cardio-only premix that lasts about 12 minutes and is pretty interval-oriented.
Kick Max has a great 15-minute Blast Challenge sequence that consists of 10 mini-intervals with precisely next-to-zero recovery in between, so your heart rate always stays up there.
Just my suggestions -
A-Jock