I took a Princeton Review course for the GMAT and took the GRE at just about the same time, killing two birds with one stone. As easy as the GRE actually is, I considered it money well spent. The fact that it's easy means you should do really well with smart preparation for the exam. Don't panic over the math -- it's not difficult. Doing practice exams is fantastic preparation in itself.
I picked up a book of tough vocabulary words, using the exam as an excuse to learn as many new words as possible. If the GRE relies as heavily on vocabulary as it once did, this might actually be a sensible way to prepare, but it is quite time-consuming. I saw many words on the exam that I had learned in my review, making me glad I had gone to the trouble. I don't think it's bragging to say that I rocked on both the GRE and GMAT, since I really think it was due to the preparation I did.
I have since forgotten many of those words. Yeah, my vocabulary has actually shrunk considerably.