Scatter Plot from Correlation
This generates a scatter plot for a given correlation based on the instructions from this page: http://www.uvm.edu/~dhowell/StatPages/More_Stuff/CorrGen.html
Note that each time you change the value of r, it re-randomizes the base data. The algorithm fails for either r = 1 or r = -1 but those cases are pretty easy to generate by hand.