Are you planning to use a multi touch table? We have developed a new solution that allows the recognition of objects with different shapes using any type of monitor combined with an infrared touchscreen frame. Resting a solid cylinder on the screen rather than a cube, you can access different content via the application.
The results obtained are similar to the Samsung SUR40 (the old Microsoft Surface), but with a much more readily available technology, far less expensive and with the advantage of being able to use a monitor of any size.