After I completed the Kaplan Math Workbook, I purchased access to the GMAX Online course and it made a huge difference. A lot of the math was a refresher at that point, but I learned a lot of shortcuts and advanced concepts that I wouldn't know otherwise. Additionally, it made it a lot easier for me to balance my Math and Verbal studies. The course is $400 for 90 views, but you can usually buy other peoples' left over views for about $200. There are only 30 videos, so 30-40 views is all you need.
Keep in mind that the videos are about 2 hours each, so it will take you quite some time to finish the course. The best part of GMAX is that it covers EVERYTHING that's on the GMAT. I watched the videos on Fast (1.5x speed) in Windows Media player and finished 1 video per weekday, 2 videos on weekends. The course took me approximately 4 weeks to complete. Each video comes with a list of homework problems from OG11, Quant Review, and Verbal Review, so you get to apply what you've learned immediately.
Best of luck!