New HSK: Complete Vocabulary Lists: Word lists for HSK levels 1, 2, 3, 4, 5, 6 (on Amazon)
Integrated Chinese: Simplified Characters Textbook, Level 1, Part 1 (on Amazon)
For advanced learners:
Literature and Society: An Advanced Reader of Modern Chinese - Revised Edition (on Amazon)
Having trouble with your pronunciation? Download Audacity on your computer (a free audio MP3 player/editor) and record yourself speaking some Chinese words. Compare your pronunciation to the audio clips on Yoyo Chinese's Pinyin chart. Do you sound the same? It's often difficult to hear how you really sound when you speak, but much easier when you listen to a recording of yourself. Practice speaking Chinese and listening to yourself daily.
Having trouble remembering how to write Chinese characters? Try making up a little story for each component of a difficult character. For example, the bottom part of 篮 lán from 篮球 lánqiú (basketball) kind of looks like a net from above (皿). The three ⺮ zhú radicals could be players competing for the 'ball' (those two leftover lines on the left) around the basket (皿). Maybe it's a stretch, but you'd be surprised how much your imagination will help when memorizing all the 2,000 characters required for basic literacy in Chinese.