The Creative Edge by Mary Todd Beam.
Acrylics Unleashed by Glyn Macey – some interesting mixed media projects described step-by-step. She uses paper in compositions containing architecture very effectively. Acrylic Revolution and Acrylic Innovation by Nancy Reyner (Innovation includes a dvd). Here is her website http://www.nancyreyner.com/ She really embodies what is possible with all things acrylic. She collaborates with other artists in Acrylic Innovation to really provide learning opportunities for exploring acrylic paints, mediums, and how they interact with other possible components of art. I really think if you are making collage with acrylics and want to teach yourself with less error in your trials, her books and videos are worth spending some time with.
Just Paint It by Sam Piyasena Lots of great techniques and instructions.
The Painting Workbook by Alena Hennessy. Her website is http://www.alenahennessy.com/