Lord of the Rings Trilogy--Extended Edition
These movies had just come out when I started collecting DVDs, and once I heard these extended cuts were in the works I held out for them. I was floored by the sheer amount of extras and added footage, and the quality is still top-notch. Even though the Blu-Ray version has a nice, thick gold box that looks great, I still give the edge to the DVDs for their book-like spines and quality box art.
Blade Runner Ultimate Edition
I waited years for a decent edition, then this came along. All the cuts, together in one nice package--in a briefcase nonetheless, with a folder of quality artwork and swag. It was far more than I expected, and it still brings me joy.
Planet of the Apes Ultimate Collection
Having the five original movies, the 2001 remake, the TV show, and the cartoon all bundled together gives me immense satisfaction, and the discs even come with a good heaping of bonuses. The bust is a little flamboyant, but it still sits on my shelf like a nerdy effigy, and I've become quite used to addressing it as Caesar.
Dawn of the Dead UHD
Thank goodness this showed up to me recently, intact, after being missent to Thailand. This thing is a beast with its sheer number of discs (three cuts of the movie, extras, and three CDs of music, holy crap). Plus books. I think this one has the most number of discs for a single movie I own, but it's also a dang good box.
Columbia Classics Volume 1 UHD Collection
A decent selection of films in decent quality, but I'm most floored by the box, the way it unfolds, and the way it houses the individual movies.
There are a bunch more I could list, it's hard to settle on just five.