Topology (Flow chart) drawing program

Does anyone know of a flow chart program that I can use to diagram parts of my network in ASCII. (i.e to e-mail a description to someonme) I should be able to type in a description (that shows up in the block) and then specify links to other blocks, the program outputs an ASCII block diagram suitable for putting into documents. Im sure someone must have written something like this when they were back in undergrad :) geoff white