SquirrelFish Extreme (SFX)
The people behind the best HTML engine around (yep, that's WebKit for those that don't know it yet) just announced the next generation of their new Javascript engine, SquirrelFish Extreme, just a few months after SquirrelFish itself was announced and before it was even adopted in any product. In the performance chart they posted in the linked page the engine is around 3 times faster than JavascriptCore and two times faster than SquirrelFish. Impressive.