I've been a long time fan of Dia.
Both the Windows and Ubuntu version worked good enough to suffice my diagram needs.
I just turn it on and place all the diagrams into position to later paste them onto any document. Some people like Visio better and I'm sure it is, but my interest was in using a freeware tool that didn't required a license for something that I deemed as very simple.
Well.. there is no Dia for Mac. There is an expensive replacement for Visio on OSX but I'm still interested in good and free solutions.
Looking around the web I've stumbled on a very neat application: yEd.
This graph editor is simply perfect for my needs. Runs in Java and I could start right away for a try without installing it on my machine. The design is very intuitive and thought there are some things that might take one hour or two to get used - it is very easy to use without the need to read any sort of manual.
That's the type of program that I like, free and simple.
This editor can handle UML and a lot of goodies that someone in software development will surely enjoy.
If you're in need for a simple diagram editor, you find it here: