Mod Podge Original 16-Ounce Glue, Gloss Finish Party Supplies, 16 Oz, 12 Pieces An old standard for applying your decoupage images
Martha Stewart Crafts Decoupage Paper Cutouts, 33301 Botanical Floral (78-Piece) Pre-cut imagery is available at your craft store and in books like this one
New Decoupage: Transforming Your Home with Paper, Glue, and Scissors Go beyond knick-knacks and use decoupage on your doors, walls, or furniture!
K&Company Jubilee Adhesive Borders Pre-cut borders are really pretty when incorporated into painted moldings!
Decoupage: A Practical Guide to the Art of Decorating Surfaces with Paper Cutouts Well-regarded book on decoupage - great for beginners!