I'd suggest you hit your local libarary. There are lots of books and magazines with hobbyist projects. Pick one that appeals to you and go for it.
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Search "Arduino" here on Instructables. There are some very awesome doo-hickies here. One of my favourites is the Knocking Block.
What are you interested in knowing more about? Pick a project. http://www.google.com/search?q=mini+digital+projects&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a