My favorite itread is iBiClimb. It is co-coahed by two of itrain's best coaches - Grace and Keith.
It has intervals of treadmill (walking/jogging or running - you choose), elliptical, and resistance training for which you step off the cardio machine. It is a very effective and fun total body cardio + weights circuit.
For pure treadmill cardio, use the descriptons to find a workout in the itread library of the length that you fancy. Sonme are flat and fast, some are hilly, some mix both. I have yet to met an itread for treadmill that I dont like. I dont like the outdoor itreads though.
For iClimb and icycle pure cardio - again anything coached by Keith Irace is the best in my opinion. Keith uses the beat of the music in very clever ways and is a encouraging, energetic coach with no drama.
iTri Set 8 is a super long cardio workout of 70 minutes that has you use the treadmill first, then the elliptical, the cycle and then back to te treadmill for a home stretch.
Of the cardio + weights circuit workouts you will find them in the itread or the iclimb library. For circuit workouts that uinvolve just one cardio machine, I like the two iTread ballet workouts, and iclimb Circuit Surprise.
I also like iSculpt traditional circuit workouts with Mimi.
Sorry, I did not help much.
I have a large itread library because I subscribed for almost 2 years and I enjoy my collection. If you click with it, you are likely to collect more than one.
~* Vrinda *~