Hi quasemsm,
The most realistic CATs on the market are the 6 Official GMAC CATs, although there are other 3rd-party CATs that will provide you with a reasonably accurate score result (assuming that you use the CATs correctly). While it might be tempting to take lots of CATs, doing so is NOT what will make you a better Test Taker. A CAT is just a 'measuring device'; actual improvement comes from study, practice problems and quizzes, review, etc. The CAT is a way to measure your progress.
1) How have you scored on each of your CATs (including the Quant and Verbal Scaled Scores)?
2) What is your goal score?
3) When are you planning to take the GMAT?
4) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich