It's been a while since an official count, but I own about 1200 DVDs, 300-ish VHS tapes, a couple dozen LaserDiscs, two UMDs (just for collecting sake), two VCDs (now I'm just getting needlessly obscure) and exactly one Blu-Ray (because it was a release only available as a BR/DVD combo).
Though I was a film student and am versed enough in classic, foreign and arthouse cinema, my collection (and indeed, my passion is life) is primarily B-movies, cult flicks and exploitation. Of course I have an appreciation for the likes of Kubrick, Bergman, Godard, Ozu, Tarkovsky, etc., and I could answer just as honestly by saying something 'respectable' like 'Blade Runner', 'Brazil' or 'Taxi Driver', but my favorite movie will always be 1985's 'The Return of the Living Dead'.
In a nutshell, it's got a clever, original story (introducing many components which are now an integral part of zombie fiction), it strikes a pitch-perfect balance between horror and comedy (I'll always prefer very dry black humor in horror over broad slapstick like 'Shaun of the Dead'), it's very well-paced and edited (never a dull moment even though the zombies don't even come in until halfway through the running time), the characters are all unique and likable (likeable characters is the number one (and most forgotten) rule of writing good horror movies) and the acting is far better than necessary, the production design is fantastic (an atmosphere vividly inspired by 1950s horror comics), the special effects are phenomenal (the "Torso" zombie puppet is a masterwork) and the soundtrack is incredible (primo '80s punk and deathrock). Overall, it's just a blast of a film and a definite highlight of what I consider to be the golden age of modern horror (it pretty much all went downhill in the '90s).