Oh man, 2 way tie here. One daily, one pre-workout.
First, the daily staple: KSM-66 ashwaganda. I was first exposed to ashwaganda while using Kaged Muscle's test booster. I felt really good, better than I expected. I was using the product as PCT for 8 weeks of ostaplex, and wasn't expecting my energy and overall strength to keep going up afterwards. I now feel better taking 1200mg daily that I have at any other time in life, physically and mentally (stress is a passing thought, not a clawing distraction). I have been buying the Nutrabio release of KSM-66 for the last few months, and will continue to do so as long as they carry it.
The second item is Condemned Labz Convict pre-workout. This one really works well with me. Not too much caffeine, dialed in focus. No feelings of hypertension or over-stimulation. I'm also able to sleep at night after wearing myself out. Its almost a ritual at this point. My body knows what expected of it after 2 scoops; pushing myself to the sweaty edge of my ability. Another product I'll buy as long as its produced.
Both of these products have boosted me more than anything else I've used, both physically and mentally.