Alot of these players had careers that most people would be proud of, when I think of under rated, I think of someone who did more than anyone expected of them.
With that said, to me, Bill Sampy could be the most under rated WR we ever had. Made clutch catches, quality character, and was an excellent blocker (a role that he accepted in 2005 without any complaints). As important as Babb and Fenroy were in 2005, none of the run we had would have been possible without a veteran WR who could catch and block on the outside to give Fenroy some extra room to operate.