We have several resources that we recommend to students who are particularly interested in strengthening their vocabulary. The first of these is our Vocabulary eBook, which goes nicely with our vocabulary flashcard app (which itself contains 1000 must-know GRE words!). We also have a separate vocabulary builder app that ties everything together :)
Once you've made your way through the Magoosh material, we also like Barron's 1100 Words You Need to Know. We wrote a review on how to get the most out of Barron's, which you can read right here.
But don't stop at vocabulary lists to improve your vocabulary! Reading is the best way to improve your vocabulary and verbal skills. Reading from high-quality sources such as the following is a great way to reinforce new vocabulary:
If you work on your vocabulary and read an article or two a day (as well as a book or two!) during your studies, you'll be in good shape when Test Day finally arrives. Good luck!