Damn! I was just about to start a thread like this.
Maybe it's because I'm from Colorado, but I love the Colorado flag and Denver's flag.
Another Colorado flag I'm on the fence on is the City of Loveland's flag. It's unique and has a good idea behind it, but it's too far out for me to really like.
I also redesigned Longmont, Colorado's flag for the hell of it. Here's that.