For in-flight I find it hard to beat my
lip light, not too bright, hands free, and always shines where I look. For preflight, and general use I use a
small flexible LED light from streamlight. Great for hard to see spots, and you can mount it on your kneeboard for in-flight use, though it's really too bright for dark night flying.
Plus there's always my mandated crappy pt. 135 flashlight.