1 HDD of 4TB for videos/series/a few live DVD (and a few movies, but I'm not a movie person anw).
1 HDD of 2TB for music only (available today: 1,16 TB). On it, folder for the musical style (OST, Black/Trash, Gothic/Sympho, Industrial/EBM, VK, J-pop, J-rock, K-pop, Metal, Rock/RnB/Pop, Visual Kei). On these folders, name of the artist/band, then a folder for each release (example: 2XXX.XX.XX / release name - CDS/EP/LP // and I keep the log detail when I rip myself a release), a PV folder (and a gallery folder according to the band, megamasso for example; and in it, folders for each member and group photos) and that's it.
I keep it organized, because I am a maniac.
I'm using iTunes to listen and organize everything, but not all are in it. I put mostly those I listen the most (but I've got the majority of it on my iPod). I also bought the other week CDpedia/DVDpedia to collect all that I have and to keep track of my collections, it will be long to add everything but I will do it.
CDPedia + megamasso (in french):