I didn't have time to take a class when I needed to prepare for the GRE. Here is what got me a tuition waiver & teaching position: vocabulary flash cards. Purchase a GRE-word dictionary and make flash cards or just read the book. The verbal section is a killer.
I have some friends that took GRE classes and it boosted their scores about 100 points or less, but these classes can be time consuming and expensive. If you need a quick and easy way to survive the GRE verbal section, I suggest the flash cards.
Also, think long and hard before going to grad school. I received a great education, but if you've only been a full-time student you might want to get some work experience under your belt before or during grad school to keep you sane.
Best of luck!