Replacement for Visio
At one client, I needed something like Visio to digitize some whiteboard notes, particularly some diagrams and flows.
Since all I really needed was a way to draw boxes and connect them with arrows, I went looking for something cheaper. I googled "visio replacement", and found Dia: http://live.gnome.org/Dia
The user-interface is a little strange, but not too difficult to figure out. The primary oddity I noticed is that in order to export to a graphic (i.e.a PNG to import into the Wiki), you have to scale the image as much as 250% first. You do this through the Page Setup menu.