It has been said a picture is worth a thousand words! There have been a large number of softwares to write dsp codes and analyze signals and algorithms. It will be good to share on data plotting tools, that is - given a data set (1-d, 2-d, 3-d, ..higher dimensions (creative ways to visualize this)) what are the different tools available and advantages of each for plotting such data sets. Advantages can be with respect to: (a) quick/easy plotting (b) formats of fugures (.eps, .svg) file which can be generated (c) latex font embedding easiness (d) post script figures Tools like: matlab, octave, gnuplot, tikz, pgf etc are widely used by many of us. It would be useful to share your experiences (advantages/disadvantage) and best plot you have drwan using the tool you prefer!
I guess Python has great tools for this, especially IPython Notebook: http://ipython.org/notebook.html . It has good visualization opportunities and at the same time you could document your code and make it re-configurable and online. Of course it best for visualizing data low dimensions and creative visualization algorithms can be prepared either in OpenGL or high level languages such as MATLAB.
In 3D, if appropriate, time varying surfaces can be embedded in 2D and shown as a 3D volume. For generic 4D visualizations you could either use videos, or accumulated volume maps. For visualization of high dimensional data, always make sure you check methods such as Multi Dimensional Scaling.