GetRobo has pointed out a new website by Francisco Paz, which focuses on his experience building an open source personal robot called Qbo. From the few images on the site Qbo looks remarkably well made and quite similar to NEC’s PaPeRo, meaning it might be used to experiment with image processing, speech recognition, speech synthesis, and (assuming it has wheels) obstacle detection and SLAM. He also mentions in his blog some of the open source software that’s out in the wild such as OpenCV, Festival, and Sphinx, which would allow you to do some of that.