I use Org Mode for emacs. Each project idea gets its own org file in an all-project-ideas directory. Each file is added to an Org Mode meta-file that specifies the location of the org files.

I go through my ideas directory about once a week to keep things fresh.

Org Mode has built-in outlining support, date tags that bring items onto your calendar in several ways, and a ton of other features.

I tried it out for GTD a few months ago and got very quickly hooked. Until then I had been planning on writing my own web-based system.