My personal faves:
Circuit Max done exactly as produced; OR you can do leg-circuits only by banging out barbell squats, plie squats and lunges during the 2:00 resistance cycles (bring your towel and your water - this one's a sweatfest);
Gauntlet, from the Intensity Series Terminator Disc - this one has step/interval step, Boot Camp floor interval-cardio blasts, leg, combo lower / upper body, and upper body resistance cycles;
High Step Training Advanced (HSTA) - lotsa 2:00 nosebleed step cardio with lotsa leg presses and lotsa great upper body
Low Impact Circuit; stick on the Blast-Only add-on (which gives you a bonus fourth blast that I've developed great respect for)
A favorite leg circuit mish-mosh from yours truly (this works best with a 3- to 5-disc changer):
Step warm-up of choice (my favorites are Rhythmic Step's and Body Max 2's); THEN
CTX Power Circuit step-circuit segment; AND/OR
Body Max Original's power circuit segment; AND/OR
Body Max 2's power circuit segment; THEN
Boot Camp cardio-lower body only premix
HTH -
A-Jock