Plenty? I can think of only four. Granted, my knowledge is probably limited, but I can't think there are more than a dozen, many of which are small and inconsequential.
More importantly, how many of these non-muslim terrorist groups have attacked the United States? How many have dedicated themselves to destroying us?
I'm gonna regret this. I've been a student of the Mid-East, Arab politics, and Islam, for decades. I take a backseat to nobody in my distrust, dislike, and desire to totally defeat and crush our enemies in the Islamic world. But as a historian, I gotta say that Islam does not hold a monopoly on terrorism. In fact, the first hotel bombing directed at Americans I recall was in Sagion -not a hotbed of Arab unrest. Ireland has produced at least four terrorist groups, and Spain has two? Columbian narcoterrorist count in my book, as do those from Puerto Rico. The HUKs killed Americans with great pleasure, and the Shining Path were known for brutality. Bader-Meinhof, the Red Army Faction, and the Italian Red Brigade loved killing Americans. The worst attack on Lod airport was by Japanese terrorist, and Entebee was a joint action by Bader-Meinhof and Palestinians. Most of these groups had help from the Soviets, who woulda loved to destroy us. Wheew.
But given all that, I agree that the Islamic threat is larger, more prolonged, and most dangerous.