Being a young 'un I can only speak from 1999ish onwards. My list in no particular order and with (hopefully no Leeds bias);
Dave Furner- hard as nails
Shontayne Hape- Make my life misery as a young Leeds fan misery, appreciate him now though.
Lesley Vainikolo- See above
Ali Lauitiiti- one of the most consistantly exciting players
Willie Poching- solid servant to all he played for, not spectacular but gave everything he had
Stanley Gene- again not spectacular but a legend in his own right
Jamie Lyon- great ball handler, kicker, all round RL player. Still doing it at the highest level today
Joe Vagana- Part of the Awesome Foursome at Bradford, a 130kg wrecking ball.
Steve Renouf- one of the greatest centres ever FULLSTOP
Brett Dallas- another tough cookie, with lighting pace

There have been great players to play in Super League e.g. Stacey Jones, Andrew Johns, Danny Buderus but I don't feel they contributed enough to the English game to warrent a place on my list. Just opinion

Henry Paul
Jamie Lyon
Joe Vagana
Stacey Jones
Adrian Lam
Lesley Vainakolo
Brett Dallas
David Furner
Adrian Vowles
Robbie Paul.

A slight Bradford bias, but i've chosen overseas signings, not just players. People that have done a lot for their clubs.

I know. I was really looking forward to seeing him play but obviously I couldn't say he was best I saw at such a short stint. Thought he was one of the best classy centres I've seen though when he played SOO and for Aussies tourists

steve carter
julien oneil
Kurt Sorensen
Dale Shearer
Emosi Koloto
Esene Faimalo
Robert Relf
noel cleal
kevin tamati
david peachy

Suprised no ones put Jason Smith,was with us for 4 years,the 1st 2 seasons he was simply superb....single-handely destroyed Leeds and Gave a master-class on loose forward play at Wigan when we drew there,his last 2 seasons was wracked by injuries but a truly superb Ball playing 13.

in no order and with a slight biased to my own club:

Les Boyd
Kevin Tamati
Andrew Johns
Allan Langer
Phil Blake
Jamie Lyon
Mal Meninga
Tuigamala (spl?)
Kevin Iro
Henry Paul