GMAT Club Tests

Honestly these tests are on another level. They aren't written exactly like the GMAC tests, but they test the same skills. These tests go above and beyond though to include little things that may have not been considered. In truth, these tests will take your quant score to the next level. The biggest criticism I have would be the explanation of some of the harder questions. If you don't have a strong foundation, it will be difficult to understand the most difficult problems' explanation. I would recommend really delving into the forums and trying to establish a background for these specific questions. All in all gmat club is a great resource.