Nadim has released Asciio, a Perl/GTK application that lets you draw ASCII charts using a GUI. Objects on the screen are sizable and have all the properties you'd expect in a drawing tool (titles for the boxes, bullets, etc), but the end result is plain text that's embeddable in your code.
Here's the first of two screencasts that give you a feel for its capabilities.
Nadim says "I find myself starting it quite often just to draw a little diagram that helps me write better Perl code. Then I can keep it in the code itself."