I have used following and my preference for materials are
1) GMATClub Challenges (25 for $79) ,
Best Math questions ever if you finish 25 challenges and can solve each and every questions 49+ is yours.
2)
Manhattan GMAT CATs (3 for $24)
Very good Test and explanation, though some questions were too time consuming to be in real exam!
3) Kaplan CATs
Good tricks and though questions in both Math and Verbal, just don’t believe their scores.
3) Princeton Review CATs (Same rank as Kaplan)
Nice thing about this CD is you can create multiple logins and keep giving tests. As test is adaptive you may find big overlap if you are really improving. Though, some questions may be repeated.
One other software I have used and really liked is Cambridge CD(~20$). They have around 5-6 CAT and I would place them before Kaplan and Princeton!