Good question. Its a nice change to get away from all the drug talk for a minute! Here are some supps that I use. I'm not sure if I want to consider protein as a supp. I look at that as a food, but I do use it. More in the off season and cut them out in prep. I always use whey ISO. 

In order of importance :

Multi. I've been digging the beverly super pak. IMO, they are better than the animal pak. I notice my urine stays bright green for a full 24 hours with the beverly pak, leading me to believe that it has a slower release than vitimans that leave me pissing clear a few hours later. 

Fish Oil. Year round, I stay on 3-5g year round. I should really look more into mercury free fish oil, but at this point, I haven't. I can tell the most differecne in contest prep when I forget my fish oil. It's anti-inflammation qualities keep my joints feeling good when I dry out. 

Fiber. I use a sugar free psyllium powder year round. In the off season, it's important to keep the food moving through my system so that I can continue to eat more. In contest prep, when carbs are lower, I'm not getting as much fiber from my foods so it becomes even more important. 

Probiotics. I use probiotics year round to aid in digestion and promote healthy flora in the gut. I've also found that they improve my skin. In contest prep, I tend to get acid reflux and these help. In the off season, I drink keifer plus use a high quality probiotic cap. In contest prep, I cut out the keifer. 

In contest prep, I also use Vit C 1000mg and a B complex. 

Those are the most important supps that I use. Besides them, I will also use creatine mono and BCAA intraworkout. I use BCAAs during fasted cardio, if needed, but during prep, find that they sometimes mess with by blood sugar, since leucine can spike insulin. If I'm tired, I may use a preworkout supp to give me an extra boost, but don't rely on them.