One of the most interesting side stories in the NFL between now and the start of free agency next March will be how what will happen with a potentially powerful receiver class.Michael Crabtree and the San Francisco 49ers will surely be watching closely.There are 10 receivers who are poised to be free agents after the year that have to be considered top-flight wideouts. Crabtree is one of them.ESPN Insider Mike Sando polled general managers and coaches to put together a ranking of the top 10 potential receiver free agents.