Have you heard of mind-mapping? I find that it's been the most successful at allowing me to "dump" my thoughts on an idea or topic, and push it out of my resident memory. It's even more powerful than a to-do list because as you think more about the idea, you can flesh it out by making new child nodes in the tree. That way, you can be sure that you capture everything, so once you've dumped your thoughts, you can truly "let go" without fear of forgetting something.

They make apps for it on phones, so you can keep it with you wherever you go. Might be worth a try!