This is just like Whittaker's Words, but it doesn't crash so often

Latin Lexicon might be my new favorite, it has English to Latin, Latin to English, a word study tool, feedback, usage... it's great

This website is terrific as a word translator as well as for glossing any parts of speech a Latin word might fall under.

Create your own study sets, search for ones already created or join the class. Features flashcards and games to study. Mainly used for vocabulary

Great resource for Greek and Latin texts. Also has a word study tool imbeded in the text so you can learn about a word's grammar while reading.