I've started my own design notebook to keep my design ideas in one place. I just grabbed a simple 50 cent notebook from the "back to school" sale and got to work. Some of them are original ideas, several are ideas I've made or plan to make that are from others sites around the interwebs.
I've drawn little graphics of the finished object (trust me, these are very rough drawings!) Also illustrations on how to draw the pattern pieces, and how to cut out the bits and assemble. Scribbled some directions and tips and tricks on what to do once you get all the pieces cut out...
Might as well keep these ideas for later, and best I not forget what I did!