shameless plug
And for those who can speak Chinese, i.e. know the grammar but are limited to pinyin and can't type in Chinese characters there's this handy tool that combines pinyin input with a dictionary (and frequency table) and makes it easy to write in Chinese. Basically just type the word in pinyin and then choose the right chinese character from the suggested word list. The English definition of the word helps to choose the correct Chinese character. There is support for traditional and simplified.