I have used Matlab for data analysis and plotting, but have investigated that the Scilab can perform simirarly to some extend, which is known as a mini version of Matlab.
If you are convenient with programming and looking for open source then you should go for Python and R for analysis and plotting. Particularly for plotting and grid data analysis you can go for Generic Mapping Tool (GMT). It provides bet quality graphs and full control where you can plot anything as you want. I personally use GMT for plotting.