TOD
I'm not a "completist". In most categories, I collect only what means the most to me personally; neither space nor funds will allow it any other way. I'm actually getting better at this. For a few years I was grabbing everything in sight, almost hoarder-style, and I'm happy to say it's been much more gratifying to learn to narrow things down to that which is truly meaningful.
The most "active" collections:
Movies (and a few TV shows) on BLU, DVD, LD and a few remaining Beta/VHS (nearly 3,000 titles - not discs, but individual titles - across all formats).
Music (recorded): Some 1200-1500 LPs, about 100 reel-to-reel tapes, and oddly enough, just a few hundred CDs in which the main growing segment is Kritzerland. If money was no object, the CD collection would have grown by orders of magnitude, but for the most part I content myself with the damage I can do right here.
Music (scores): Broadway, opera, orchestral, some piano.
Books: Music, movies, TV, plays, certain Disney stuff, movie tie-in paperbacks from the '50s-'70s, a small selection of Modern Library, lots of by-and-about Poe and Proust, mid-20th century travel and regional stuff, various and sundry other things. For general fiction and literature -- just a handful of firsts, a lot of Heritage Press, "annotated" this or that -- mostly, those editions that appeal and make the most sense for me, without regard for actual value.
I could expound in detail over all the parts and sub-parts of the above, but these collections aren't that large or impressive in comparison to others here and I'm just trying to keep it general.
To be continued...