DataGraph is a simple and powerful graphing application for Mac OS X. It is a great companion for Excel, Numbers or any of the big statistical packages.
Simple because it is very easy to draw plots, bar graphs, and fit functions. Start typing in data and the graph immediately shows up. Pick from the initial template list and modify the data, change colors, resize easily and interactively.
Powerful because as you use DataGraph more and more you will see that every aspect can be tweaked, both interactively and by specifying exact values. You can zoom in on a particular spot, attach labels, compute histograms, fit functions, overlay experimental and analytical results.
Because of DataGraphs separation of data and graphs you can then very easily create the same graph for different data by just importing or pasting a new data set into the data table.