BBC1 have continually showed the original 'Halloween' on the night itself for at least the past 3 years now.
Other than that i find it hard to, you do have those 'halloween horror marathons' freudstein mentioned, but sadly they don't last too long.
I just keep a day to day look out on Sky Movies Sci-Fi/Horror and The Horror Channel, which you can find showing classics such as An American Werewolf in London and Hellraiser 1/2 i've noticed lately.
The 90's were better, especially Nickelodeon and such, which would ALWAYS without fail have the halloween episodes of every show on, Sabrina the Teenage Witch, Are You Afraid of the Dark etc...