Słownik Polskiego Slangu - Polish Slang Dictionary (Polish-English)
Online dictionary of Polish slang. Based on Maciej Widawski’s Corpus of Colloquial Polish, it also represents probably the most comprehensive treatment of nonstandard Polish.
Introduction to Russian slang and scientific analysis thereof
Русский мат с Алексеем Плуцером-Сарно (Russian)
Official website of Alexey Plutser-Sarno, leading Russian specialist of slang. A must if you understand Russian.