If you haven't taken the opportunity to check out the fifth edition of ExcelTips: Amazing Array Formulas, you might want to do so in the near future. I released this new-and-improved edition about ten days ago, and the special sale will be ending in just a few more days.
What does that mean? It means that after Wednesday the price on this valuable e-book will return to normal (not a bad price, even then), but through Wednesday you can get your own download for 30% off the regular price.
ExcelTips: Amazing Array Formulas provides great detail on how you can use array formulas to calculate results in ways you can't do with regular formulas. Some folks have called array formulas a "regular formula on steroids," and with good reason; they are super powerful! They allow you to perform calculations on large amounts of data in a single step.
You can find more information about this new edition here:
Remember: the sale ends on Wednesday, so don't delay!