The Heteronym Homepage - resource about words that are spelled identically but have different meanings when pronounced differently
Vocabulary Links - Detailed Links to Words and Phrases - all levels
Topic Vocabulary - Vocabulary by topic, including Sports, Music, Movies, Time, Numbers, Holidays and Festivals, the World, Buildings, Family, Etc.
The Visual Dictionary Online - "an interactive dictionary with an innovative approach. From the image to the word and its definition, the Visual Dictionary Online is an all-in-one reference. Search the themes to quickly locate words, or find the meaning of a word by viewing the image it represents."