Already mentioned but definitelly have to mention again:
Douglas Adams
Philip K. Dick
For anyone not familiar with Philip K Dick, you'd be familiar with movie adaptations of his stories. He wrote mainly short stories in the 50's to 70's and more than likely while on drugs.
Films:
Blade Runner... based on the story
Do Androids Dream of Electric Sheep?
Total Recall... based on the story
We Can Remember It For You Wholesale
Minority Report... though does deviate from the book in a few places.
Screamers... based on the story
Second Variety
Impostor... written in '53, adapted to movie twice, in '62 and again in 2002(with Gary Sinise). One of my favourite short stories, probably because it was the first PKD story I read, tho from memory was only about 3 or 4 pages long.