I took N.O.-Xplode for a while. It does what it says, though it may be the caffeine and the sugar giving you the boost, while psychologically you're also motivated to do extra reps.
In any case, it has some creatine in it, retaining water (could be a good thing or a bad thing depending on your build and goals).
I've finally landed on not taking any supplements, and eating a lot of chicken breast without the skin (roughly 34g protein and 6g of fat). If I were to go back to any supplement, it'd probably be a multi-vitamin.