The upside of revving the engine is that you go a little faster. The downside is that you get a bigger dose of work and recovery is harder. The exception is probably caffeine, which doesn't so much as rev the engine as improve fat burning which improves endurance. It's the go-to supplement, well-tested, and it works.

Beyond that, for the experimenter, there's:
Potassium nitrate - no nasty taste and nasty cost problem like with beet juice, same nitrate
L-Carnitine L-Tartrate
Glutathione
Citrulline Malate
Beta-Alanine
Sportlegs

See www.examine.com for more info on the various chemicals.