A supplement that many are aware of but is often overlooked is caffeine.  Taken pre-workout, aside from the added energy boost, caffeine has been shown to increase overall strength, stamina and aid in fat-burning.  In fact, almost all commercial fat burners on the market contain some level of caffeine.  Some studies have shown that taking caffeine pre-workout has also shown to decrease muscle soreness.   On training days, try taking 200-400mg about 30-60 minutes before exercising.