I've never really put down my favorite films of all time. But I'll try...
1) Nightmare Castle (1965) starring Barbara Steele. Gothic horror cinema at it's finest. I only discovered this movie a few years ago on a public domain DVD collection and was drawn into a world of haunted castles, paintings of dead beautiful women and the true golden age of horror film.
2) Tales of Terror (1962) starring Vincent Price. The Roger Corman-Edgar Allan Poe cycle was the American answer to the British horror cycle. Vincent Price is so good that he can read a McDonald's menu and make it sound like Shakespeare.
3) Curse of Frankenstein (1957) starring Peter Cushing. The film that started the British horror cycle (1957-1974) and it's the best one. Doctor Frankenstein is not a sympathetic figure as portrayed in Mary Shelley's novel, he is a pure sociopath who has no qualms about robbing corpses and even murder. You can't help but cheer for Peter Cushing here.
4) Mulholland Drive (2001) directed by David Lynch. Every time I watch this movie, I notice something new with it. The best "dream within a dream" film ever made.
5) The Empire Strikes Back (1980). I know it's cliche to say that ESB is the best Star Wars movie, but it is. This represents the best of the saga when it was at it's peak.
I have so many other "favorite" movies that I can only list the rest as honorable mentions:
Night of the Living Dead (1968), The Wicker Man (1973) starring Christopher Lee, Nosferatu (1922), Fright Night (1985), Pulp Fiction (1994), Grindhouse (2007), The Last Man on Earth (1964) starring Vincent Price, Dracula (1931), Frankenstein (1931), 2001 (1968), Full Metal Jacket (1987), The Watchmen (2009), Star Wars (1977), Dawn of the Dead (1978), Day of the Dead (1985), Soylent Green (1973), Zardoz (1974), The Omega Man (1971), Planet of the Apes (1968), Raiders of the Lost Ark (1981), Metropolis (1927) directed by Fritz Lang, Black Sabbath (1963), A Fish Called Wanda (1988) starring Kevin Kline, Raging Bull (1980), Evil Dead II (1987), The Two Towers (2002), Fellowship of the Ring (2001), Excalibur (1982), Escape From New York (1982), The Brain That Wouldn't Die (1962), The Terror (1963), 1984 (1984), Star Trek I (1979), Carnival of Souls (1962), Citizen Kane (1941), Birth of a Nation (1915), The Searchers (1956), Lost Highway (1997), Reservoir Dogs (1991), Horror of Dracula (1958), The Abominable Dr. Phibes (1972), Brazil (1986), Bride of Frankenstein (1935), The Body Snatcher (1945), Son of Frankenstein (1939), The Mummy (1932), Cabinet of Dr. Caligari (1920), Vampyr (1932), Count Yorga (1970), Dracula (1979) starring Frank Langella, Scarface (1983), Common Law Cabin (1967), All Quiet on the Western Front (1930), Rocky (1976), Rocky III (1982), First Blood (1982), True Lies (1994), Psycho (1960), Clerks (1994), Rasputin the Mad Monk (1966), The Innocents (1961), Goldfinger (1964), Demons of the Mind (1972), Targets (1968), The Shootist (1976), Twins of Evil (1971), Phantasm (1979), Alien (1979), Last House on the Left (1972), Girl Slaves of Morgana Le Fay (1971), Freaks (1932), The Sadist (1963), City of the Dead (1960), Blood From the Mummy's Tomb (1971), House on Haunted Hill (1959), Comedy of Terrors (1963), Asylum (1972), The Blair Witch Project (1999), Dracula A.D. 1972 (1972), Tower of London (1962), The Fly (1986), The Wrestler (2008), An Evening of Edgar Allan Poe (1970), Masque of the Red Death (1964), Zombie 2 (1979), Saw (2004), Scars of Dracula (1970), Madhouse (1974), Vanishing Point (1971), Dr. Phibes Rises Again (1972), Creepshow (1982), The Oblong Box (1969)
I have a hard time judging my favorite films against each other. If I really like a movie, I buy it. But B-Horror movies are definitely my favorite genre, so the top 3 above is pretty solid for me.