This is why I moved a huge portion of my TODO list into an IDEAS list. This is an outliner document (Org-mode) that contains notes on lots of different ideas.

So why didn't I just delete those items? Because writing down that stuff helps me not to think about it the whole day if I don't want to.

The IDEAS list grows and grows, but that's okay. I don't feel obliged to implement any of these ideas. Whenever I recall an idea, I go to that document, add some notes, and that's it. No deep research, no domain buying, no name searching. Just writing or extending on what comes to my mind, and roughly structuring it.

From time to time it happens that I do want to implement one of these ideas. And in that case I have some nice, simple spec to start from.

As a side note, I started to do that after I read "Writing, Briefly" from Paul Graham (http://paulgraham.com/writing44.html), which contains the following great advice:

    ...
    when you finish, leave yourself something easy to start with;
    accumulate notes for topics you plan to cover at the bottom of the file;
    don't feel obliged to cover any of them;
    ...

These points are applicable far outside the scope of writing. In that sense, my IDEAS list is the clearly separated "bottom" of my TODO list that contains the "accumulated notes".

As a final note, this concept seems to be somehow related to the Not-To-Do list that some people advocate.