The National Park Service has a great web resource commemorating the 150th anniversary of the American Civil War.
The site offers a state-by-state breakdown and description of every battle that took place. To see the Pennsylvania page click here. For details on the Battle of Gettysburg, click here.

Pennsylvania has its own site dedicated to learning more about the Civil War.  Civil War Pennsylvania 150 (CWPA 150) is a statewide partnership of major history organizations convened by the Pennsylvania Historical and Museum Commission (PHMC) and the Pennsylvania Heritage Society (PHS) to develop programming and content for the commemoration.  For more details on this effort, click here. 

And finally, the Gettysburg National Military Park has a wealth of information, educational programming and special events to commemorate the famous battle.