Criterion by spine.
Everything else: Genre-- then alpha

on the top of my dvd cases, i have my tv shows, dvds w/ slip covers, and digipacks organized by height and then alphabetical. tv shows facing outwards are in no particular order.

then i have all my other dvds alphabetical except i separate the snappers and the keepcases.

Got my Zombie flicks in alphabetical then everything else in alphabetical.

Though my collection is currently in alpha order by title I've had it organized by director's name before. It was time consuming to do but sometimes you just want to mix it up (and it's a great procrastination technique).

I don't organize my collection. It's in the order of when I first bought each disc.

At the moment, alphabetically by genre. I have my movies spread out through several different locations, so that has been the easiest way so far.

I got westerns and criterions in one place. The rest are kind of scatered. Then I have 24 or so storage boxes and they are by studio.

I organize mine by using shelves.

I do alphabetically as well. But sometimes I get the urge to organize by genre. But so far I've been too lazy to do that.

Alphabetically and by Genre:

Action/Adventure
Drama
Sci-Fi/Fantasy
Horror
Foriegn Film
Comedy
Childrens
Western
TV Shows (live action and animated)
Special Interest (Documentaries, Wrestling dvd's, etc)

Mine is all in alphabetical order also. Except all of my movies w/ sequels are together. For example, Friday the 13th 1-8 and then Jason Goes To Hell & Jason X. I like to keep them together.