The best thing I have used is a Petzel headtorch. Get the one that has 3 x led's in it. Powered by 2 AAA's lasts for about 120 hours plus. It gives enough light to check the outside. Inside it is great, all you have to do is slip it over your head and guess what you have both hands free. I always wear it ( switched off ) when night flying just in case. Incidentally it is that small that you can hold it in your fist.
It costs about £ 20 from mountainering shops