Omaha Public Library has an excellent web page with links to their digital collections. The collections are Early Omaha: Gateway to the West, Trans-Mississippi & International Exposition of 1898, Nebraska Memories, Early Nebraska and World Stereoview Collection.
I am particularly interested in the Early Nebraska collection which contains maps and atlases for the United States, Nebraska and county maps and atlases. If you are interested strictly in Omaha maps, be sure to check out Early Omaha: Gateway to the West.
The time periods for the maps and atlases varies, but some are from the mid 1800s. Many of the maps are for adjoining states, such as Colorado, Kansas, Iowa and the territories of Dakota, Idaho, Montana and Wyoming. They are excellent when trying to place your ancestors in a location at a specific time.
If you are interested in purchasing maps from the library, contact them at 420-444-4800 or firstname.lastname@example.org. Be sure to provide them with the image number.
While you are on the Omaha Public Library web site, be sure to check out information about their genealogy reference collection. There are nearly 8,300 items. This is also a "must" if you are planning to visit the library.