I thought you'd never ask

The minimal system I use is:
1. Ideas and Potential ToDo items must get written on (3x5) INDEX CARDS, one card per idea, with date written prominently on the card).
(a notebook is NOT a viable alternative; only an index card will work because only index cards may be easily and independently shuffled, sorted, laid out neatly).
2. Never try to keep anything in memory -- immediately log ideas/todo items to a card to get it out of mind. Ideally you should not act on cards immediately -- give yourself time to decide the idea is not worth pursuing.
3. Keep TWO collections of cards -- one should be easily accessible at all times, and consist of cards still under active consideration. The other is a storage collection for cards that have fallen to such low priority that they could be thrown away (just throw them away if that doesn't bother you; i find keeping them in storage less traumatic).
4. Occasionally go through your active consideration collection and organize cards by project/theme, and move cards to the storage collection. Paperclips can be useful to group cards logically.
5. When working on a project, grab the cards related to the project and lay them out and decide which ones you can tackle. When a card is completed it can be thrown away.