Like many editors, I keep a notepad and pen within easy reach when I am in the car, and my wife gives me a look that I could never describe when I grab all the free newspapers/magazines at every stop when we take a day trip or longer journey.
I think many newer editors, editing in general topics, rely more on submissions. New editors editing in specializing categories often bring a lot of knowledge of where to hunt for good URLs.
When I do go hunting for sites, I love to dive headfirst into the free webspace sites like yahoo, geocities, tripod and the like. Those sites, which are generally noncommercial, are usually labors of love and while their design leaves a lot to be desired, they are quite the treasure trove of information. And, since then are not professionally managed sites, the users rarely submit to search engines or directories.
With the thousands of active editors, representing every possible demographic and geographic variance, it is difficult to generalize.