Let's start with the online collection of Nebraska Virtual Exhibits which include:
And that's just a sampling of what's available.
Other pages display highlights from the Nebraska Historical Society's photograph collection covering farming, industry, daily life and more, including a small sampling of photos from the 1890 massacre at Wounded Knee.
Nebraska Treasures includes WWII Posters, cowboy and Indian artifacts and photos, and baseball paraphenalia.
There are more treasures at a second site and Nuestros Tesoros (Our Treasures) devoted to Mexican-American heritage in the state.
You can use a search tool to search many of the records and indexes at the archives, though it's not entirely clear what is and isn't included in the search.
There are also searches for specific collections, indexes and topics including:
A page of additional database searches includes:
Overall, this is a real scattershot website and there's no way I could list everything of value. It's worth spending some time exploring its nooks and crannies as it does have some unusual materials that will interest historians, genealogists and the generally curious.