flashlights of all different kinds. LED, incandescent..... from kids to flashlights to law enforcement type, battery operated, wind up, you name it. Cell phones, Timex indiglo watches, laptop computers, laser pointers, speed lights, glow sticks (from your friendly neighborhood dirty hippie festival)......
Pretty much anything that emits light. Use multiple sources for one exposure. Be creative. Everything is going to give off a diffrent temperature of light, which makes for some really neat effects.