Books. I think that I'm close to having 200 of them. I find that books allow you to understand a performer and their style. Reading something by Paul Harris is different than something by John Bannon which is different than something by Tom Stone. @FunkyBottoms and @FlipMagic86, reading the Marlo books is VERY different. I also enjoy the Miracle Factory books about some of the classic performers - Roy Benson by Starlight and The Secret Ways of Al Baker. Then there are the historical classics - Martin Gardner's Impromptu and Greater Magic. My favorite book is Jim Steinmeyer's Conjuring but his book Technique and Understanding is amazing. Card College, Art of Astonishment, Tarbell, The Books of Wonder are all great sets in their own way. I love the pure theory books like Larry Haas's Transformations, Magic and Meaning, Scripting Magic, Maximum Entertainment, the Show Doctor and the books that present magic with meaning like Tales of Enchantment, Life, Death and Other Card Tricks, This is Not a Book - OK anything by Robert E. Neale, or Eugene Burger. Anything by members of the Madrid school of magic: Ascanio, Tamariz, Giobbi and others. And then the compilations - Jinx, Apocalypse, Hirophant, Collected Almanac, Tailsman, Chronicles and more.
That being said, I have some amazing DVDs but they probably are not what you think. The best DVDs I have are focused on a single prop - Levent's DVDs on Linking Rings, Miser's Dream and Billiard Balls, Ammar's DVDs on Cups and Balls, Jeb Sherril's DVDs on Zombie Ball and the L&L DVDs on Zombie Ball, Bill in Lemon and others. Those just compile so much information in one place that you can use them to build your own personal routine.
I could tell earlier you had a nicely curated set of books, LOTS of excellent references I'd love to avail myself of! I'm still finishing up Hollingsworth's Drawing Room Deceptions from the last time you mentioned it.
You mentioned Ammar in the videos. I always wonder if others think his style is as corny, stiff and forced as I do. I love the guy, he's brilliant and is definitely a 'modern' classic in his own right, and he's worked with and is respected by many of the greats (the Dai Chronicles come to mind?). I blush with pseudo-embarrassment watching him perform though.
Lastly, I grin with envy every time I watch a Jason England vid. That library over his shoulder in many of them is beyond envious. Lots of very expensive 1st editions in there, and a vast collection. Man how I'd love to peruse that collection as well!