For me, there are two series where I particularly noticed a difference in my appearance, despite no changes in my diet (which I would describe as an okay diet, but not great). Those two series were the S&H series and the 2006 series (Butts and Guts, BodyMax II, etc).
A few years back, I did a three week on/three week off bit of the S&H series for about six months and saw huge improvements in my strength levels. In terms of my appearance, I would say that my arms, in particular, got bigger and showed more muscle. But the biggest impact it had on me was really in terms of my ability to lift heavier weights--something which has continued to impact me positively on other workouts to this day, despite the fact that I don't use the S&H series as much as I once did.
Then this past fall I finally decided to do a full rotation with the 2006 series. I did a five week rotation, and saw a difference in my physique. Overall, I developed a leaner, more toned look. My body shape is one where I don't look lean or toned quite naturally, so it pleasantly surprised me to get those results. And, because of that, the 2006 DVDs rank as my favorite of the Cathe DVDs.