United States Conference of Catholic Bishops - Advent Season 
The USCCB website provides a wealth of resources for the Advent Season, including an interactive Advent Calendar, podcasts, reflections, and other activities. 

National Catholic Educational Association - Advent Resources
The NCEA offers a variety of Advent activities for educators, students, and families.

Roman Catholic Diocese of Portland - Advent Page
Advent resources and links provided by the Diocese of Portland.  Highly recommended by the NCEA.

Advent Catholic Prayers & Advent Activities for Kids
Advent-themed resources and activities from Sadlier Religion's "We Believe" blog. 

An Advent Guided Reflection on Emmanuel – God with Us
From Joe Paprocki's blog "Chatechist's Journey: Sharing the Journey of Teaching the Catholic Faith"

Holy Heroes Advent Adventure
A collection of free Advent resources and activities geared towards children ages 5 to 12.