From the 1950s through the 1980s, grindhouse movie theaters threw anything on-screen that could turn a dime, from badly dubbed foreign imports to exploitation quickies padded with stock footage. Sex, sadism, sin, and shock were what sold, and even the worst miscarriage of cinema could make money with the right title and a gratuitously gruesome poster.

Now, the movie sewage that used to gush out onto Times Square is flooding the New Release shelves of your local Blockbuster. Recently, numerous DVD companies such as Blue Underground, Something Weird Video, Image, and Synapse have been releasing deluxe DVD editions of the sleazy features that once played the scummiest theaters on earth. And some of them are even good.

Exploitation veteran Albert Pyun has recently repurposed himself as a self-proclaimed auteur, and his latest straight-to-video flick is “Left for Dead” (2007), a gothic-horror-Western packed with female gunfighters. It’s an unbeatable concept, but we’re dealing with the man who directed “Cyborg” — the Jean-Claude Van Damme movie that even morons hate. In this hack’s hands, “Left for Dead” becomes a classic example of everything evil about exploitation: great concept, great DVD cover, boring movie. It’s a movie so cheap that you never even see anyone shoot a gun; instead, they jerk their prop pistols to dubbed bangs. But that’s exploitation filmmaking all over.

England used to provide plenty of horror fodder for American drive-ins and grindhouses, and that tradition continues with the Irish-British-Danish co-production “Shrooms” (2006), a slightly more satisfying “Just Say No” teen horror flick. Five American kids head to Ireland, where a hunky local takes them into the woods to pick magic mushrooms. But after the kids dose up, they discover that the woods are haunted by ghosts from a school for troubled youth, and they spend the rest of the movie running, screaming, and dying. “Shrooms” stands head and shoulders above rubbish such as “Left for Dead” and “April Fool’s Day” (a poorly conceived, straight-to-video remake of the 1986 slasher film of the same title), but its director, Paddy Breathnach, has a weak grasp of the mechanics of exploitation. Grindhouse films should start strong and end strong, but Mr. Breathnach forgets that he’s supposed to be a sideshow carnival barker, and actually takes his by-the-numbers screenplay seriously. The result? Too much time spent setting up plot twists and not enough time delivering the good stuff, such as the talking death cow.

“Them,” on the other hand, is a grindhouse gem. Foreign movies typically go straight-to-video these days. Ignoring subtitled movies at the multiplex means avoiding a bunch of boring arthouse 101 films, but reading subtitles is essential on the straight-to-video scene. French shocker “Them” (2006) is a cinematic fun house full of mysterious noises and dark corners that spends 20 minutes setting up its characters and the next hour sending them tiptoeing down dark hallways, sprinting through spooky forests, and crawling down fetid tunnels. Few movies have this firm a grasp on the simple physics of horror, and “Them” manages to wring maximum tension from something as small as a slowly turning doorknob, a flickering shadow, and a shoe stepping cautiously onto a creaking board.

A horrific home-invasion movie of the highest order, “Them” is as blunt and simple as its title. No script, no real story, and no character development — just one dread-inducing scene after another. The film did receive a perfunctory theatrical release, but its real home is on top of the straight-to-video pile.

That’s also where “Altered” belongs. It was dumped straight-to-video in 2006 by cowardly distributors, and that’s a crime. A bunch of country-fried Southerners were abducted by aliens before the movie begins, and when we catch up with them years later, they’ve become a gang of paranoid, gun-toting emotional wrecks out for revenge on the aliens who probed them. After capturing a little green man, they decide to torture him to death, “Hostel”-style, but then realize that killing the Martian will invite genocidal repercussions from his colleagues.

Directed by Eduardo Sanchez, the co-director of “The Blair Witch Project,” “Altered” takes a single idea and runs with it all the way to the finish line — something most Hollywood films don’t bother to do these days. It’s genuinely suspenseful, funny, creepy, and delightfully over-the-top (where else can you see man and alien duke it out?).

“Altered” and “Them” represent the best of what you can find in the straight-to-video ghetto. Down in the muck, beneath copies of “Flight of the Living Dead,” “Transmorphers,” and “Senorita Justice,” down deep in the new grindhouse ooze, it’s still possible to find gold.