"R" is a free, open source software package that does an amazing number of things with and for statistical analysis, data processing, modelling, graphing, and so on. In overall functionality it's similar to stuff like SciLab and MatLab. I happen to find R more intuitive to use. And it's cooler :-). And there are hundreds of scripts, packages, etc. provided by happy users.
The biggest drawback to R is probably its name, which is essentially impossible to Google around. So, here's some links to very handy pages.
The main page is cran.r-project.org
This page contains lots of great links, some of which I've listed below:
graphics from published packages
A stunning collection of graphics submitted by R enthusiasts the world over (including me).
R mailing list archives; there are many mailing lists which one can subscribe to via the cran.r page above.
I'll be posting more of my R-toys and goodies as I get a chance. For now,
short.R is a spiffed-up version of 'head' plus 'tail' (unix commands) to display the first and last few values in a vector or matrix or dataframe.
rotrw.R does the infamous Rot-13 encryption algorithm, but jazzed up: you can rot by any value, and select whether to rotate over just the alphabet or across the full basic ASCII character set. Warning: may be subject to export controls (yeah right).
bdrun.R , basically a cheap pseudoscreensaver to calm the soul. (Almost as good as unicorn chasers). Note-the "bd" stands for "Birthday," in homage to a pre-1980 FORTRAN routine of that name which produced this sort of plot.
Here is a neat (albeit much slower than, say mapply.R) thingy I wrote to do windowed functions. It's like a boxcar averager but you can load it up with pretty much any function you want (so long as it's a function of a single variable, basically).
Here are a couple examples of what my very own clplot.R routine can do (it's available in the plotrix package). The color of the line depends on the y-axis value (something, incidentally, which is next to impossible in Excel). The user can select the levels at which the color changes, the color sequence, etc.
a little sinc^2 function
random data vs random data