John describes his filing system for his CDs, and so I shall do the same. Because, well, why not?
The largest unit I own has seven shelves (you can see it behind me in this photo). Part of the top shelf is used currently for items that don't fit in the other units, like double-disc sets of filmscores and the like. Next comes the Celtic music collection, which takes up about two-thirds of one shelf (currently about 70 or so discs). These I arrange alphabetically by artist, with multiple discs by artists arranged in order of release. After the single-artist CDs come the compilations, which are arranged alphabetically by title.
Next comes classical. These are arranged alphabetically by composer, starting with Leroy Anderson and going all the way down to Meredith Wilson. Within each composer's ranks, works are arranged roughly by type: symphonies first, followed by concerted works and then chamber music or instrumental solos, with operas, oratorios, cantatas, and large-scale choral works coming last (but not least).
At the end of the "main" classical section comes discs that aren't themed by composer, but by type of album. Here I have orchestral compilations, followed by wind ensemble/wind band compilations. Then there are the chamber compilations, followed by solo instrumental compilations, and finally solo vocal compilations.
Now, one problem that arises with classical is what's a compilation and what isn't. I have a CD, for example, of Van Cliburn performing two piano concertos: the Rachmaninov Second and the Beethoven Fifth ("Emperor"). Since it's only two major works on the disc, it doesn't really feel like a compilation -- but then, where do I put it? With Beethoven, or with Rachmaninov? My general approach with CDs like this, when the two or three works on the disc are of comparable heft (in terms of running time on the disc), is to go by the first work on the disc. In this particular case, that means I keep the disc with the Beethoven CDs. (Of course, the trouble that arises is that I sometimes forget that this disc has the Rachmaninov on it, so I don't listen to Van Cliburn's Rach Second as much as I do either of my two versions by Vladimir Ashkenazy.)
Sometimes this is pretty easy, though: if a CD has a long work by one composer paired with a short work by another, it goes under the composer of the long work. Multiple operas are filed in alphabetical order by title.
That takes care of the freestanding unit. Beside this unit I have a plastic spinning unit that is designed to hold two hundred CDs. However, this design assumes that one uses the little grooves in the unit to store them flat; I discovered that it actually will hold even more if I ignore the grooves and just stick the CDs in there upright. Here is the bulk of my film music collection, arranged alphabetically by title. (The discs in this unit start with scores that begin with the letter 'C'. The A's and B's are found elsewhere. More in a bit.) Now, I'm a bit loose with the "By title" bit: I group the three CDs of the Omen Trilogy scores together, even though in strict alphabetical-by-title fashion, I'd split them up with the second one first, the third one second, and the first one last. But for the most part I stick to the titles. At the end of those, I have more compilation albums. These I split out into single-composer compilations, filed by composer, and then into multi-composer compilations, which are filed alphabetically by title. (Lots of film music fans, like John, arrange filmscores by composer. I don't do this, although not for any real reason -- I've just always done it this way.)
Then I have two cruddy "sliding drawer" boxes. These contain my "New Age", jazz, and "vocal" selections, as well as the A's and B's of the film music. I rarely buy any New Age or jazz anymore; ditto the "vocal" stuff (here's where I keep my Sinatra, Bobby Darin, Bing Crosby, and the like). There is also a free shelf on the entertainment center where all of my specifically Asian music resides: Asian classical music, anime soundtracks, Canto-pop, and the like. Tucked away on the same shelf, but behind the Asian stuff, is the Christmas music.
Finally, I have a bunch of CDs that are currently sitting haphazardly on the bookshelf beside my writing desk. These are special favorites of mine, for which I want to find a very special location near my writing desk so I'll always be able to stick them into the Discman while I'm working. I haven't come up with anything yet, so there they sit. Among these discs are my Lord of the Rings recordings, the Star Wars scores (along with several other John Williams favorites), my Solti Der Ring des Nibelungen, the live Colin Davis Romeo et Juliet and Les Troyens by Berlioz, and the like.
And none of this takes into account the CDs that I have laying about in an unfiled state.
So there you go. And to think, when I went to college for my freshman year, my CD collection consisted of a grand total of nine discs.