They say that ideas are "a dime a dozen" and that it's the execution that matters. However, there is no chance of ever executing on an idea if you keep forgetting about all those gems you come up with.
To keep track of ideas I have for apps and websites, I find that trello is perfect for quickly inputing, and keep them organised.
I've previously tried notebooks and google spreadsheets, but I found them to be clunky and rarely used. In contrast, trello is almost always open in my browser.
I have three columns setup in trello. The first list all the ideas that I currently have floating around.
In the second column I move over any ideas that I'm bullish about and am in the process of product design - these ideas might never go to production - I often discover a fatal flaw or an awesome competitor during the design stage.
And finally the third column has the ideas that are "work in progress" and are actually being executed on.
This is a screenshot of my ideas board. p.s - I have no qualms sharing my ideas, as the killer details are hidden in the description and I do believe that execution is everything.
Every couple of weeks I go through the list and move any ideas that I'm bearish on down to the bottom and anything bullish gets pushed up to the top. Trello's ability to drag and drop the ideas up down the list, with such ease, is why I use it.