How about David Boston?
(And all the kids go, "who?")
Dude was unguardable his ProBowl year. One man wrecking crew. I think he (and TO) opened the door for some of these other huge WRs that probably would have been considered too big for the position prior to their success.
Like Ward, he's at the end of the road, but being a Packer fan I have to nominate Donald Driver. A nobody out of Alcorn State (I think), wasn't even supposed to make the team and they just couldn't get rid of him. He just became the Packers all-time leader in receptions and yards. And almost all over the middle...dude is humble as they come but tough as nails and a throwback Packer.