Vatican
The Vatican web site.
This is an extremely comprehensive site. It is not always easy finding material but it is usually there. The search engine is a full text search on all Vatican documents. So if your not sure what document you need do a key word search for it.

USCCB
The United States Conference of Catholic Bishops
This site has over 30 departments ranging from Liturgy to an online version of the New American Bible to the Catechism, a real wealth of information.

U.S. Catholic Dioceses
Dioceses Index from The United States Conference of Catholic Bishops

Archdiocese of Philadelphia
The web site for the Archdiocese of Philadelphia

The National Association of State Catholic Conference Directors
A State Catholic Conference is a Church agency representing the dioceses within a state in order to provide for the coordination of the public policy concerns of the Church. Thus, a State Conference of the Church communicates with state governments, other Church Agencies, non-Catholic churches, and secular agencies. Bishops, priests, religious, and lay persons are involved in the work of the State Conferences.

Pennsylania Catholic Conference
The Pennsylvania Catholic Conference (PCC) is the public affairs arm of Pennsylvania's Catholic bishops and the Catholic dioceses of Pennsylvania.