In terms of sheer ability, I'd say GI is my favourite (non-Warrior/Kiwi, of course) player to watch. When he is on, there's very, very little and opposition can do to stop him. Absolutely amazing.
Having only seen Tomkins more or less through highlights packages, I have to say I don't think there is a better natural runner of the ball in all of League. Some of the stuff he can do is just amazing. Currently is a non-Warrior, though I sincerely hope that is going to change very soon.
In terms of players who are always there keeping their team up beat, first one to be there to congratulate and pump-up his team mates, I marvel at Beau Ryan; he gives absolutely everything to every performance and is always encouraging his teammates.
As far as un-sung hereos go, I like the Kevin Kingston's, Corey Parker's, Matt Ballin's and Shaun Fensom's of this world - just give absolutely everything every game.