Most genealogists are aware of the common genealogy websites (Ancestry, FamilySearch, USGenWeb, etc.) to use when they are researching. Another website--though not focused on genealogy research at all--is extremely valuable to researchers in Maryland: Internet Archive.
The purpose of Internet Archive is to "[offer] permanent access for researchers, historians, scholars, people with disabilities, and the general public to historical collections that exist in digital format." Many universities, historical societies, and other organizations throughout the world have donated materials to this website for digitization and storage.
If you are researching in Maryland, there are quite a few useful collections. The site includes collections of material from the libraries of the University of Maryland, St. Mary's College of Maryland, and other libraries around the country that hold material relevant to Maryland studies, including the Library of Congress and the Allen County Public Library.
City directories are vital for research in urban areas, including Baltimore City. Among the Baltimore city directories found on the site are those from 1812, 1822-1823, 1831, 1833-1834, 1835-1836, 1837-1838, 1842, 1845, 1849-1850, 1851, 1858, 1860, 1864, 1865-1866, 1867-1868, 1868-1869, 1870 through 1892, 1890-1891, 1893-1894, 1901, 1905-1906, 1903 through 1909, 1912 through 1915, 1917, 1918-1919, and 1920 through 1923. [Tip: Some of the earlier volumes are titled Matchett's Baltimore Director.] These directories have been digitized by various repositories.
By searching for the name of one of the most prominent nineteenth century Maryland historians, J. Thomas Scharf, you can find several of his history books, as well as his reports to the General Assembly while he served as the Commissioner of the Land Office for the state.
- The Chronicles of Baltimore: Being a Complete History of "Baltimore Town" and Baltimore City ... (1874).
- History of Maryland from the Earliest Period to the Present Day ... (1879).
- History of Western Maryland, 2 volumes (1882). Covers Frederick, Montgomery, Carroll, Washington, Allegany, and Garrett counties.
Scharf also wrote several additional history books that may be of interest, and have been digitized:
- History of Saint Louis city and county [Missouri] from the earliest periods to the present day ... (1883).
- History of Philadelphia, 1609-1884 (1884).
- History of Delaware, 1609-1888 (1888).
- History of the Confederate States Navy from Its Organization to the Surrender of Its Last Vessel ... (1894).
The Internet Archive site also contains other books of historical significance to Maryland:
- The Calvert Papers, Number One (Baltimore: Maryland Historical Society, 1889).
- Rev. William P. Treacy, Old Catholic Maryland and its early Jesuit missionaries (Swedesboro, N. J.: St. Joseph's Rectory, 1889).
- George F. Bragg, Men of Maryland (Baltimore: Church Advocate Press, 1914). This book concerns the history of African Americans in Maryland, and contains biographical sketches of influential people of color throughout Maryland's history, including Ira Frederick Aldridge, Benjamin Banneker, Scipio Beanes, Daniel Coker, Frederick Douglass, William Douglass, Henry Highland Garnet, Hezekiah Grice, James Anderson Handy, Frances Ellen Watkins Harper, James Theodore Holly, William Levington, James W. C. Pennington, Eli Worthington Stokes, Harriet Tubman (Davis), Thomas M. D. Ward, Alex W. Wayman, Samuel Ringgold Ward, Harrison Holmes Webb, and Lewis G. Wells, M. D. The book also reprints writings and speeches by several of the profiled figures, and a few other texts important to Maryland African American history.
- St. George Leakin Sioussat, Ph.D., "The English Statutes in Maryland," Johns Hopkins University Studies in Historical and Political Science, Series XXI, Nos. 11-12 (Baltimore: John Hopkins Press, 1903). This monograph discusses the British legal system in use in Maryland during the colonial period, especially focused on the Resolutions of 1722.
- James McSherry, History of Maryland (Baltimore: Baltimore Book Co., 1904).
- Annie Leakin Sioussat, Old Manors in the Colony of Maryland, First Series and Second Series (Baltimore: Lord Baltimore Press, 1911).
In addition to these historical works, you can also find some books of genealogical abstracts and indexes, including:
- Leslie and Neil Keddie, Wicomico County, Maryland, Wills, Liber WB#1, December 1867-Deceniber 1879 (Salisbury, Md.: Family Tree Bookshop, n. pub. date).
- First Methodist Episcopal Church, Baltimore, Maryland, Records, Volume 1 (unknown pub.)
Even more significant, however, and less known to many researchers, is that the Allen County Public Library has digitized a number of the microfilms of records produced by the National Archives and Records Administration. These microfilmed records include federal census records, Baltimore passenger lists, and records of the field offices of the Freedman's Bureau. Though not indexed, these publications provide free access to original federal records for Maryland (and other) genealogists. You can access these records by searching for "Maryland" among the collections of the Allen County Public Library Genealogy Center in the Internet Archive.
Even if you are researching in other locations, the Internet Archive should be considered a must-view site.