If/when you want to create new adventures, there's a number of resources on the web. If I recall correctly one was "The Netbook of Plots". Just ideas to get thoughts flowing and fleshed out.
There's lots of good advice about creating adventures to search for on the web as well.
At a more advanced remove, if you want to create a world (loads of fun, but not where I would start), there are a series of old Dragon magazine articles called Dungeoncraft that were released years ago. Very good.