If you've worked your way through all of the Magoosh material, I'd like to begin by congratulating you! You're clearly a hard worker and a dedicated student. Good job! You've already made a big step towards getting a great GRE score :D
Alright, so now you'd like to practice some more. Let's talk about what other resources you can use!
First and foremost, I'd recommend that you use as much official GRE material as you can. This material is published by the ETS. This is the company that writes the actual GRE, so they are very good at creating practice problems that are similar to the ones that you'll see on the real test.
If you'd like to do full length practice tests, I'd suggest that you take the two free, official GRE PowerPrep ii practice tests. You'll need to download the PowerPrep ii software in order to take these tests. The ETS also has two free PDF practice tests, which you can find here and here. These two tests are a bit old - and some of the questions are the same as the ones on PowerPrep ii - but this is a good source for extra practice problems.
If you're looking for more practice questions in general, and don't necessarily want to do practice tests, you should pick up a copy of the Official Guide to the Revised GRE. This book has a lot of official practice questions, so it's an excellent resource! You may also be interested in the Official GRE Verbal Reasoning Practice Questions book, and the Official GRE Quantitative Reasoning Practice Questions book.
Know that we have explanation videos for many (but not all) of the practice questions in the ETS books and resources! You can learn more about where to find these videos here.
Finally, unofficial GRE practice tests can be a bit hit or miss: sometimes they're representative of the actual GRE, and sometimes they are not. This is because it's hard to write really good GRE practice questions. However, we do recommend one unofficial GRE prep source: Manhattan GRE. They have six online practice tests which you can buy here. They also have a free practice test here. If you'd like additional practice questions that are not grouped together into a test, you should consider the Manhattan GRE book series, or the Manhattan 5 lb. Book of Practice Questions.