I have a numbered system of folders (i.e., "0 - Ideas", "1 - Raw Mixes," etc.) that indicate where the project is in implementation:
0 is for my ideas/scratchpad,
1 is the raw mix and arrangement,
2 is for the raw stems of the project,
3 is for the fully mixed version of the project,
4 is for the fully mixed stems of the project,
5 is for the rendered mixes for mastering,
6 is for the mastering projects,
7 is for the rendered masters.
Obviously, saving several versions of several projects takes up a good amount of space, but it's easy to backup to another drive to keep my main external clutter-free. Any project that I actually do anything with (and have completed) is moved to a subfolder in 0 called "Done," so that way I don't keep checking out a project or idea I've already completed. Everything is packaged as a folder for reasons Arnaud mentioned above. It seems like a far easier way to manage projects and assets.