Ballooning spiders have been found as far as 1600 km (~1000 mi) away from land!
The babies can really fly, as high as the upper atmosphere. (alas, no numbers for how high)
Wunderbare Welt der Spinnen by Stefan Heimer. Best title ever!
Then there is the sheer awesome of an academic paper that discusses the physics of spider ballooning. (PDF) The paper goes into the economic impacts of spiders as predators on crop pests.