This is one hot, that is, cool, app — http://springpadit.com/home/ :

Springpad gives you a place to quickly and easily save anything you want to remember. Take a note, create a task, scan a product barcode and look up the book your friend mentioned. The best part is that no matter where you are, Springpad is there with you to make sure you don’t forget something worth remembering.

Big tip of hat to Refdesk, specifically its Site of the Day, where many good things pop up regularly.

That said, I must admit that consigning a great thought to such a saving bin is often to forget about it, in my experience. But how about notes for something you are working on? Instant retrieval here, which following instant saving — by e-mail, for instance — makes for a great aid to putting something together.