New HSK (Hanyu Shuiping Kaoshi) - the standard Chinese exam in mainland China. 6 levels in order of difficulty. UTF-8 encoding.
Download Now: hsk-new-111221.txt
List adapted from Lingomi, and distributed under a Creative Commons BY-SA license.
Old HSK (Hanyu Shuiping Kaoshi) - no longer in use for tests, but still popular, and with several thousand more words than the new HSK. 4 levels in order of difficulty. UTF-8 encoding.
Download Now: hsk-100428.txt
List adapted from HSK Flashcards, which also has Pleco-friendly vocabulary lists for the Integrated Chinese and Practical Chinese Reader series.
For many more user-contributed flashcard lists, see the Flashcard Exchange forum on PlecoForums.com - there are lists there for many popular textbooks, common characters, radicals, and the TOP Chinese proficiency test used in Taiwan.