I was doing my usual competitor scouting on google to check out the competition, and I noticed an adwords ad, where they had mis-typed their url. Example - they had put widget-big.com, instead of big-widget.com. I look at the adwords link and it goes nowhere. So then I do a search, and find that the url is not registered. I register the url and have a website up in about 15 minutes. Now I'm getting free traffic from a url mistype.