Well, you guys probably know mine. The Danish flag. Not because I live here, because that is not something to be proud of, but because of the history, the age and the fact it is more a symbol of joy and happiness than national pride. And no pictures, because we already have hyper sized pictures in this thread, and you can go look it up yourself.
It's tough to narrow it down to just one that I'd consider my favourite...
The Japanese flag is very minimalistic but still serves as a great representation of the land of the rising sun.
The Molossian flag is awesome, well, just because it's one of my favourite micro-nations.
The flag of Yorkshire because, even if it isn't recognized as a nation, we like to think of ourselves as independent from England (yet still thoroughly English).