The most extensive collections of Delaware maps are at the University of Delaware Library, the Historical Society of Delaware, and at the Wilmington Institute Free Library.
A valuable atlas that shows names of landowners is:
Beers, Daniel G. Atlas of the State of Delaware. . . Philadelphia, Pennsylvania: Pomeroy and Beers, 1868. (Family History Library fiche 6332689.)
There are United States atlases for the following years with excellent Delaware maps: 1790, 1810, 1823, 1838, 1862, 1878, 1884, and 1917 (Family History Library film 002083.)
The best atlas for showing changes in county formation and boundary disputes is by the:
Newberry Library. Historical Atlas and Chronology of County Boundaries, 1788-1980. Volume 1. John H. Long, ed. Boston, Massachusetts: G.K. Hall & Company, 1984. (Family History Library Ref book 973 E7hL v. 1; fiche 6051426; 3 fiche.)
Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html