Posted Wed Dec 7, 2011 9:50 PM
The first thing that comes to mind is a well-respected Chinese unlicensed game for the Mega Drive called Shui Hu Feng Yun Zhuan. It's a beat-'em-up that uses sprites ripped from other games, including Knights of the Round.
Otherwise for side-scrolling beat-'em-ups, there's the Golden Axe series, the Streets of Rage series, Final Fight CD, and Alien Storm, among others. I beat Knights of the Round a long time ago, but haven't really played the other two.