"The Collagraph print is best described as a collage printmaking technique, where the image is composed from a variety of textured materials glued to a substrate and printed either in an intaglio or relief fashion." - from EKU.
"In a collagraph, the plate is built up and manipulated by the artist, using a collage-like process which combines materials as diverse as cardboard, fabric, gesso, glue, string, sand, carborundum grit, and found objects. The artist can also draw lines into the gesso before it hardens. As a result, the plate may print as both relief and intaglio. Collagraph prints are usually pulled on a press." - from Washington Printmakers, a good site on printmaking techniques.
The Dreams series of prints that I have been putting up recently, are all utilizing the collagraph technique, sometimes in combination with other media. I am currently working with collagraphs again, now in combination with inkjet prints - I will show these when they are done. I usually like using matboard as the plate, and with acrylic medium I glue on textures like string, cloth, tissue paper, as well as utilizing the medium's painterly textures, and pressing in textures using various objects. It's a very enjoyable and non-toxic process that gives interesting results!