On demand you might say even if this isn't really horror. Thinking about it i found that i still think the old masters has written the best of this Kind. And this is a list totally without Stephen King!!! Here are my picks.
1. Childhoods End - Arthur C. Clarke
2. War Of The Worlds - H.G. Wells
3. The Puppet Masters - Robert Heinlein
4. The Kraken Wakes - John Wyndham
5. Invasion Of The Body Snatchers - Jack Finney
contenders: The Martian Chronicles- Ray Bradbury, When The Tripods Came - John Christopher, The Alien Years - Robert Silverberg, The Midvich Cuckoos - John Wyndham
1. Childhoods End - Arthur C. Clarke
2. War Of The Worlds - H.G. Wells
3. The Puppet Masters - Robert Heinlein
4. The Kraken Wakes - John Wyndham
5. Invasion Of The Body Snatchers - Jack Finney
contenders: The Martian Chronicles- Ray Bradbury, When The Tripods Came - John Christopher, The Alien Years - Robert Silverberg, The Midvich Cuckoos - John Wyndham