The main NPS web page is a barrel of fun, but they have several subsidiary and parallel pages that are almost as much fun.
The first one that comes to mind is the Harpers Ferry Center. Their web page states, "Since 1970, Harpers Ferry Center has created a variety of interpretive tools to assist NPS field interpreters. These tools include audiovisual programs, historic furnishings, museum exhibits, publications, and wayside exhibits. HFC also provides a variety of services including graphics research, interpretive planning, media contracting, artifact conservation, revision and reprinting of publications, and replacement of wayside exhibits." Yes folks, these are the people who make the beautiful folders that we get in each park in addition to other graphics and media. Very talented graphic artists, if you ask me. If I had more skill at graphic arts, that would be my dream job.
The Park Service has a rather extensive history web site. You could spend hours browsing around there. One of my favorite history pages is the NPS birthday page. It lists birthdays of National Park units in chronological order.
Another of my favorites is the park planning site. This site contains PDFs of the various park planning documents. The most interesting are the General Management Plans, which are park master plans, but there is something for everyone. It seems that whenever they want to do work in the park, there is a document. Close a trail? Document. Realign a road? Document. Improve radio communications? Document. Yes, the NPS is indeed a division of the US government. I poke a little fun at them, but even the most mundane document is interesting if it concerns your favorite park.
Saving the best for last, my favorite is The Morning Report. This really tells you what is going on at the parks and the Park Service. There is an Incidents section, which contains things such as tourists falling into the Grand Canyon, a Fire Management section, which contains lists and summaries of fires in the parks, an Operational Notes section, which contains bills and other Congressional activity, and a Parks and People section, which includes job listings and awards. It is fascinating reading for the National Park buff.