Apparently quite successful when it was first released, although still relatively unknown (even to many horror fans), Night of the Demons would make an ideal movie for a Halloween after party; it's a fun, yet occasionally freaky romp that has the added bonus of being set on the holiday itself.
Essentially a tale of teens conjuring up and then being taken over by a discarnate demonic entity (the first two Evil Dead movies would make obvious companion pieces), the film is very much of the 80's (I mean this as a good thing) in several wonderful ways. The first things that struck me when watching it were the driving, Carpenter-esque, synth score (composed by the director's brother, Dennis Michael Tenney) and the groovy, animated title sequence (which to my mind recalls bits of the "Night on Bald Mountain" segment from Fantasia); both help to set the ghoulish mood perfectly.
Thanks to some scatterings of visual flair from the director (with notable assistance from the DP and production design team), inspired effects work from a young Steve Johnson, and lively performances from the ensemble cast (whose characters are broadly drawn but still somewhat believable), the film arguably transcends its relatively modest budget and set-up, therefore distinguishing itself from the reams of genre fodder being produced during the period.
I'd say the film is worth seeing alone for the scene where Amelia Kinkade (who is now a famous pet psychic; apparently she's even met the Queen) freaks out tough guy Sal (Billy Gallo) by dancing wildly and erotically to "Stigmata Martyr" by Bauhaus, but there's also plenty more to recommend throughout the entire picture.