Tangible user interfaces (TUIs) augment the physical world by integrating digital information with everyday physical objects. Currently, building these UIs requires "getting down and dirty" with input technologies such as computer vision. Consequently, only a small cadre of technology experts can currently build these UIs. Based on a literature review and structured interviews with nine TUI researchers, we created Papier-Mache, a toolkit for building tangible interfaces using computer vision, electronic tags, and barcodes. Papier-Mache introduces a high-level event model for working with these technologies that facilitates technology portability. For example, an application can be prototyped with computer vision and deployed with RFID. We present an evaluation of our toolkit with six class projects and a user study with seven programmers, finding the input abstractions, technology portability, and monitoring window to be highly effective.