(Withania somnifera: preferably Sensoril): Stress relief, improved sleep, and performance enhancement. I take 200mg (Abyss UP) or up to 450mg (3 caps ) when I use it. Haven't used it standalone.
Rosea (standardized to 3% rosavins and 1% salidroside): Stress relief and energy (reduced fatigue). Too much is just as inefficient as too little. I prefer 500mg pre-workout or upon waking (it can be somewhat stimulating).
Bacopa Monnieri (50% Bacopasides): Nootropic and anxiety relief.
Those are the three I use most often. Sure others can throw in more options as well.