GMATClubTests

GMAT club Quant tests are the best of the lot out there. But I must agree that these tests are a bit more harder than actual GMAT. In these tests you will get many more 700 level questions than in actual GMAT. Also 700 level questions pop up quite early in the tests. But having said that, I must also say that once you get used to the critical thinking required for solving these questions, 700 level questions in actual GMAT seems like a piece of cake. Just to give an example, I have never got more than 42-43 in GMAT club tests in quant. But in GMATPrep I always got 48-49. If not due to my silly mistakes, i would have hit 49-50 i almost all of the GMAT Preps I have given.
Coming to verbal tests, though they are not as GMAT-like as you will get in actual exam, but they are worth a practice. I used these mainly to enhance my time management skills and refine my verbal strategy.