Death from the Skies!
Not scared enough by global recession, terrorism, peanut butter, or nuclear war? Death from the Skies by Philip Plait will give you many new reasons to fear, every time you look up.
Plait covers topics such as asteroid impacts, solar flares, nearby supernovae, gamma ray bursts, black holes, and aliens. He concludes with inevitable scenarios; how the Sun will die, and the cold quiet that will end the Universe.
His writing style is very understandable, frequently using analogies to show the scale of the cosmos. To get the most out of the book, you may want to learn a little about how powerful nuclear bombs are (hint: very powerful), as Plait bases many calculations on the destructive power of Hydrogen bombs or TNT. Although, you may not enjoy this book if the word 'literally' bothers you -- it's used quite often.
Plait is a noted Astronomer -- his previous book, Bad Astronomy, is a great primer to dispel common cosmic misunderstandings. Along with books, he maintains the Bad Astronomy blog for Discover Magazine, and keeps his fans updated with a Twitter account.