If you want alot of pre-mixes I would suggest going for Cathe's BodyBlast Series. She has the most pre-mixes on these and they are really challaging.
PushPull/SuperSets
Step,Jump&Pump DVD
Kick,Punch&Crunch DVD (I had this one but did not care for the legs &glutes portion, so I traded it and then just got the vhs of KP&C)
The Intensity Series are GREAT and my ABSOLUTE favorite but does not have the pre-mixes that BB does.
HTH
Kim