At the moment I am organising my folders into year/semester/subject/assignment#/program etc to keep everything nice and neat. I also make folders with all of the images/video/audio etc that any of my editing programs will be referencing. And a folder for my final submission and rationale.
i've found that system very useful. I have a single downloads folder for anything i need to pull off the internet. just makes it easier when you need to do the monthly cleanup. i only create the /year// folder once that year has passed, that way i can access my current projects without having the pain to go through another folder.
When archiving your old projects and such, i compress all rendered images into a single .RAR file. then create another .RAR with the rest of the project. that way if you are running low on disk space, you can dispose of the rendered images as you still have the original project files to do them again if needed. be sure to pack all your uncompressed video's to bring them down into the Mb range instead of the Gb. Its not nice having a single video take up 25gb of space!
Music goes into its own folder with /artist/album format. i still have 2000 songs to organise eeeeek!
Games in their own.
Personally i dont like using any medium other than hard disks to backup/archive my stuff since a single scratch can screw 4.5 gbs of data in an instant, and plus i dont like having a lot of dvds around. but then again if a hard disk blows up there goes 500gb. hehe. use a RAID setup if you can, and an external if you have one.
Like i said, sooner or later you'll see the "free space left" pie almost consumed by the evil colour blue. the system your using is optimal. i manage to free up 20gbs of space every month quickly without hassles. normally i just delete the downloads folder lol.