Ending 1: The base ending; Aperture Self-Destructs.
Ending 2: You go outside; Press against the exit door and fling the Companion Cube onto the button at map ch2_016.
Ending 3: Bad Ending 2.0; Jump into the fire pit at map ch3_004

Ending Map List: gman_ch7_002 , ch2_016, ch3_004

All these endings will lead to the same credits screen