People on Rodrigues islands heard the explosion, 3000 miles away, which to this day represents the longest distance over which an unamplified natural sound has been detected by the human ear.
Here is a google map of that distance (Krakatoa is on the right):
The eruption was responsible for lowering the temperature by around 1 degree Fahrenheit across the entire globe (on average, for the year following the eruption). In the immediate vicinity of the eruption, temperatures were lowered by 15 degrees Fahrenheit. These effects are due mainly to the dust and sulfuric acid that were spewed into the upper atmosphere, lowering the radiation that hit the earth's surface and making for awesome sunsets.
Most of this information was found in the book "Krakatoa - the day the world exploded" by Simon Winchester, one of my favorite non-fiction authors.
Here is a sweet picture of lava: