I might be a bit conservative, but I think the best medium for doodles and todo lists (and these often coincide in creative projects) is paper and pencil. It has no technical limits and if done on smaller pieces of paper, not a Moleskine or other notebook, they can be easily rearranged. I usually use the envelopes of invoices of public utility companies. This way I spare both my wallet and the environment. But the best part is getting a job done and then physically destroying the list.

Last year I decided to start collecting these shreds of paper to visualize the progress I'm making. This was how the "progress jar" was born: