Most of the information listed below was pulled from http://hometown.aol.com/chirailfan/ztransva.html , and I've only verified a small part of it. It also doesn't touch on every transit company that ever existed in Tidewater. Companies I know of that aren't listed here include the Berkley Street Railway Co., the Portsmouth Street Railway Co. (which ran from 1887-1906), and the Portsmouth Transit Company.
Norfolk The Peninsula
1866-1894 - Norfolk City Railway
1894-1899 - Norfolk Street Railroad
1899-1902 - Norfolk Railway & Light Co.
1902-1911 - Norfolk & Portsmouth Traction Co.
1911-1925 - Virginia Railway & Power Co.
1925-1937 - Virginia Electric & Power Co. (Stone & Webster)
1937-1944 - Virginia Electric & Power Co. (Engineers Public Service Co.)
1940's - Streetcars discontinued
1944-1962 - Virginia Transit Co. (United Transit Co.)
1962-1973 - Virginia Transit Co. (ATE)
1973-1999 - Tidewater Regional Transit Authority (TRT)
1999 - TRT and PenTran merge to form Hampton Roads Transit (HRT)
1891-1898 - Newport News, Hampton & Old Point Railway
1898-1914 - Newport News & Old Point Railway & Electric Co.
1914-1925 - Newport News & Hampton Railway Gas & Electric Co.
1925-1928 - Citizens Rapid Transit Co. (National Public Service Corp.)
1928-1933 - Citizens Rapid Transit Co. (Middle West Utilities Co.)
1933-1935 - Citizens Rapid Transit Co. (Virginia Public Service Co.)
1935-1944 - Citizens Rapid Transit Co. (Associated Gas & Electric Co.)
After 1944 - Citizens Rapid Transit Co.
1945 - Streetcars discontinued
1974 - Hampton and Newport News plan a new mass transit authority
April 1975 - Peninsula Transportation District Commission (PenTran)
1975-1999 - PenTran
1999 - TRT and PenTran merge to form Hampton Roads Transit (HRT)