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: