I use Google to find lists for vocabulary.
There are "Dolch Words" - the first words taught to begininng readers in America.
There are "Fry Words" list of most common words in spoken and written English.
Just found the Macmillian Dictionary (2nd Ed.) which uses "2500 Defining Words" to explain ALL of the other words in their dictionary.
And of course the "Academic Word List" (AWL) for college level text readers.