Going back as far as I've been supporting them we at one time had Shay Given, Stephen Carr, Steve Finnan John O'Shea, Richard Dunne, Damien Duff, Roy Keane, Robbie Keane. And those were supported by a lot of solid premier league players. At that time almost our whole squad was premier league players, with a handful playing in the Champions League with regularity.
There are other era's that people could make a case we were more stacked, but we had a good squad in the early 00s which has consistently declined since then (at least on paper in terms of the level our players are playing at).