Flashcards are a great tool for memorizing just about anything and they are simple to create. Just write a term on one side of an index card and the term's definition on the other side. Once you have a stack of them, you can quiz yourself to see which ones you know, putting the ones you knew in one pile and the ones you didn't in another pile. Even if you didn't know any of the terms before you started making the cards, you'll find that through the process of creating the cards you actually learned several of them.
This web site is for people studying English as a Second Language (ESL) or English as a Foreign Language (EFL). There are quizzes, word games, word puzzles, proverbs, slang expressions, anagrams, a random-sentence generator and other computer assisted language learning activities. Even though the primary focus is for ESL, native English speakers may also find some interesting things on this site. This site is non-commercial and has no advertising. TESL/TEFL teachers may want to recommend this site to their students.
Quizzes, tests, exercises and puzzles to help you learn English as a Second Language (ESL)
This project of The Internet TESL Journal (iteslj.org) has thousands of contributions by many teachers.
I like it, but I prefer free.
Paper Rater is free, no strings attached, and seems to perform all the same functions if not more. Additionally, it offers instruction in some areas that might be weak, such as vocabulary. http://www.paperrater.com/