I have long been a fan of spiders in horror and sci-fi films. The fact I am something of an arachnophobe certainly makes watching spiders in cinema even more creepy for me. Over the decades there have been a bevy of horror/sci-fi movies featuring spiders, some good and some bad.
One of the first great "spider" themed horror movies was Tarantula(1955), starring Leo G. Carroll, John Agar and Mara Corday. The special effects in this film are surprisingly good and the disfigured scientists/comrades of Professor Deemer(played by Leo G. Carroll) add an extra element of horror to the already grim and creepy story of the film.
Though garnering less praise I am also quite of fond of The Spider(1958), whose alternate title is "Earth Vs The Spider"-this film continues to make the rounds on American Movie Classics(AMC), and stars (the late) Ed Kemmer. The effects are a bit more uneven in this film, and the shriek of the monster sized spider is, admittedly, laughably absurd.
In the 1970's two more movies entered the cinematic landscape of sci-fi: The Giant Spider Invasion(1975) and Kingdom Of The Spiders(1977), the latter starring William Shatner of "Star Trek" fame. Both are campy and a lot of fun if you don't take them too seriously.
In 1990 Arachnophobia hit theaters, a movie featuring a giant and poisonous South American spider that hitches a ride to a small California town where, mating with a common house spider, poisonous spiderlings are loosed on the town, the local doctor(played by Jeff Daniels) challenged to stop the creeping eight legged monsters, all while dealing with his severe arachnophobia.
More recent entries in this genre include Spiders(2000), which appears on The Sci-Fi Channel from time to time, along with its sequel Spiders 2: Breeding Ground. Another film of interest making appearances on The Sci-Fi Channel is Arachnid(2002).
Eight Legged Freaks is also worth checking out, the spiders grown to enormous size through a local chemical spill and rendered fairly well by CGI and prominently featuring enlarged "jumping" spiders and one seriously bad ass, Airstream trailer sized tarantula.
Here's a trailer for 1958's "The Spider":
The trailer for Universal Picture's Tarantula(1955):