Via ddotdc:

WMATA planning map, dated March 1, 1968 and last revised by the WMATA Board on June 11, 1970. 

Please view a full-size, searchable version of the map. (Navigational tools are at the bottom of the map.)

On March 1, 1968, WMATA officially adopted a 97.2 mile regional system in the District of Columbia, Maryland and Virginia. On February 7, 1969, WMATA revisited the rapid rail plan and relocated three of the stations, calling instead for 97.7 miles of track. The total system cost was $2.5 billion ($15.9 billion in today’s dollars) consisting of $835 million of revenue bonds issued by WMATA, $1.1 billion in federal funding, and $573.5 million from local sources. On June 11, 1970, the WMATA Board adopted a realignment of 2.5 miles of a mid-city route to better serve the city center. This revised version is posted above. 

Metro originally had a future route planned to Dulles Airport—the final destination of Phase 2 of the soon-to-open Silver Line—the first half of which (to McLean, Tysons, Greensboro, Spring Hill, and Wiehle-Reston) is scheduled to begin service on Saturday, July 26, 2014.

This version of WMATA’s planning map also features a different path for a route that would materialize as Metro’s Green Line. The proposed north-south route through the District was set to feature a station near Logan Circle and run north toward a terminus in Laurel, Md. An alternate route trajectory, which was then being studied by WMATA, ran up-and-down 7th Street NW and featured station locations near what are now the Mt Vernon Sq 7th St-Convention Center and Shaw-Howard U Metro Stations. 

According to this map, Metro also planned for a Metro line along a route that is similar to one followed by the proposed Columbia Pike streetcar in Arlington, VA. 

Pro tip: Note how the Metro Station names have changed over time.