Adams was a very early adopter of personal computers and the Internet, reports suggest that he understood the importance of XML prior to Tim Berners-Lee promoted it as HTML and the spread of what we now know as the Web.
Adams was also an ecologist, working with zoologist Mark Carwardine to identify and record rare and endangered species throughout the world, as seen in the book "Last Chance to See."
However, it was his very clear vision of the future that (in hindsight) caught everyone's attention. For example, take a look at this opinion piece. In it, written in 1999, he accurately identifies the importance of the Internet in our lives today - not bad for a piece written when dial-up modems were the usual method of connection.
Finally, allow me to mention Towel Day celebrated on May 25th every year. This event, started only days after Adams' death, is a world-wide celebration of his life and achievements.
Alternately, there is always the recent celebration of 'Douglas Adams Day' to assuage our souls.
Douglas Adams was a writer, visionary and entertainer. May he rest in peace and fondly stay in the hearts and minds of us all.