Best software for drawing diagrams?

[Jonathan Busby]

I've been trying to add diagrams to this article, but, I've only been using ASCII, with the help of JaVE and the results are really ugly. I really need to use some type of vector graphics diagramming application as the concepts in the article are hard to express visually, especially when I'm limited to ASCII.

I need something in which one can fluidly and easily manipulate a combination of block diagrams, arrows, mathematical symbols, and other miscellaneous graphical constructs.

Any suggestions would be appreciated.

Thanks,

Jonathan