We all have an affinity for words we learn in other languages that express things much more succinctly than any word in our mother tongues. For me:
"ajeno" (Spanish) - definition: something that doesn't belong to you or you are not a part of.
I can't describe exactly why I love this word...perhaps it's the mere simplicity of the idea that has no direct corollary in English. Yet it is so understandable as one word. Come on, English...get with the program!
"eenheidsworst" (Dutch) - definition: a uniform, unimaginative piece of ground meat forced into a piece of sausage, when describing mass movements, such as pop culture.
I think this is right. It's something similar. I don't speak Dutch but was introduced to this word by an acquaintance. Sure, it's long in the German/Dutch tradition, but a fantastic idea nonetheless.
"Schadenfreude" (German) - definition: finding pleasure in others' pain (or "dolor ajeno" in Spanish!).
Everyone's first big German word. It has been overused recently in English, but that does not take away from its brilliance as a concept.
Please add others from as many languages as possible! I would love to see what English words people are fans of!