Many preaching resources are already available at several Dominican websites. Here are a few recommendations:
Center for Liturgy at St. Louis University
This resource is a comprehensive site designed for use by all members of the assembly in preparation for the Sunday liturgy. Site includes prayers in preparation for scripture reflection, reflections on the spirituality of the Sunday Mass, commentary on the readings including historical/cultural context and thoughts from early church writers, music ideas, and additional annotated links.
National Catholic Reporter
Celebration section offers useful reflections on the text.
A reflection on the upcoming Sunday text. This is a great resource for homily preparation.
Creighton University Daily Reflection
These reflections on the daily and Sunday readings are sponsored by the Collaborative Ministry Office of Creighton University and prepared by members of the university faculty and staff, lay and ordained.
Contemplative reading of biblical texts using the Benedictine practice of Lectio Divina is an excellent beginning step for any preaching preparation. An introduction to Lectio is presented by Fr. Luke Dysinger, O.S.B., of Valyermo Abbey in California. The method presented here can be used individually or in a Bible study or preaching preparation group.
Stories Seldom Heard
A website of the San Rafael Dominicans with seasonal reflections.
Principles of Catholic Social Teaching (Brisbane, Australia)