One of the scariest TV programmes I have ever seen was the BBC serialisation of John Wyndham's The Day of the Triffids. The first episode begins with this guy waking up in hospital to discover that i) everyone else in Britain has gone blind and ii) the place is over run with walking carnivorous plants. Even the title sequence was terrifying - creepy 20th century classical music playing over images of newly blind people looking a bit pathetic, before one of them is hit in the face by what turns out to be a stinger from a walking plant.
There is an interesting piece on it today on the BBC, prompted by the fact that some fuckwit has decided that the programme needs to be remade: Why the love affair with man-eating plants? The article situates the Wyndham's book in the great genre of global disaster fiction, pointing out that it came out shortly before Richard Matheson's I Am Legend. Take that Yanks. For real creepiness, though, scroll on to the reader comments, and check out what one G Ben of London, UK has to say.