The sources I use include:
The Preachers' Exchange is a great website for Catholic preachers, by Jude Siciliano, OP. Well worth adding to your Favorites list.
Celebration, published by NCR, is my favorite homily preparation type service, though it describes itself as a "comprehensive worship resource." It is an ecumenical and multi-cultural resource, has very fine scriptural scholarship and homily starters, interesting and useful articles and features, a daily Mass supplement. Overall, a lot of liturgical and preaching bang for your hard-earned buck!
Prepare the Word is an online resource published by True Quest, whose strongest asset is Alice Camille, one of its writers, but whose weakest link is customer service and subscriptions.
Connections, published by Media Works and edited by Jay Cormier, is a great resource: a couple of short stories, fables, news events that relate (some more, some not quite so much!), but which provide only a springboard for your own preaching...
This Sunday's Scripture is published by Word Press and is one of the best available resources. Good exegesis and pastoral application, and some useful homily starters. This resource is grounded in a prayerful weeklong approach to the Sunday scriptures and preaching.
General Liturgical Resources worth having on your shelf:
Living Liturgy 2009: This is a comprehensive liturgy planning guide, with great homiletic resources and reflections for each of the various liturgical ministries to use throughout the week.
Companion to the Calendar: Mary Ellen Hynes' book on the calendar is the best available. I actually think it may have been written for young people, but it reflects the broadest scholarship, a global sensitivity, and awareness of civic and seasonal calendars as well as the liturgical calendar.
Jerome Biblical Commentary: If you want to dig deep into the exegesis of the Sunday scriptures, why look any further? The New JBC is a great investment, and you get a good upper body workout just by carrying it around with you!
Preaching the Lectionary: Reginald Fuller's work on lectionary preaching is one of the best one-volumes available. Ecumenical, smart, and a quick one-page-per-Sunday read.
General Preaching Links and helpful resources:
Here are some interesting preaching blogs worth exploring:
Father Mike Boutin is the co-pastor of the Church of the Blessed Sacrament, Walpole, MA, and travels widely, leading pilgrimages throughout the world to various Catholic religious sites. He is a frequent speaker on liturgy, music, spirituality, and pastoral ministry.