Mac users have a wide variety of tools available for data analysis. Via Macs in Chemistry, here is a software list. While there are some very expensive programs on the list (such as Mathematica), the median price looks to be zero!
Many of the programs linked above allow you to produce two-dimensional graphs from a list of datapoints. But what if you have a graph and want to determine the datapoints that were used to produce it? This could be thought of as the inverse of graphing data. To do this you need a program like GraphClick, which at $8 is a real bargain. I have found it to be very useful, since few academic papers make their data available.