GTD Advanced Workflow diagram
Origin story: This was the first significant thing I ever shared online. I have been a huge fan of productivity books. I started with Franklin planners, then Steven Covey, and then David Allen. When I read GTD in the early 2000s, there was an existing flowchart, but I wanted to make my own. It was supposed to be just for myself as a handy GTD binder cover insert. When I was done with the design in 2004, I was so happy with it that I shared it with David. He liked it and put it on his site as a free downloadable file. Shortly afterwards, I received emails asking if people could translate it into other languages. It ended up being the first thing that showed up if I Googled my name. In the years since they've made their own really amazing "all on one page" poster.
Here's a pdf. Hope it helps!
NOTE: My diagram is meant to be a reminder of the GTD process. If you aren't familiar with GTD yet, I would start with the book, Getting Things Done, or the GTD website.