Other key players: Osman (M), Baines (LB), Anichebe (F).
Actually Leon Osman was a very important player who played anywhere across the midfield, covering when Arteta & Cahill especially were missing. With Carsley having been sold - pending any summer purchases I guess he will be very much a first choice next year.
Arteta is Everton's creative genius while the presence of Tim Cahill is also extremely important to their attacking potency. Lescott (who also plays Centre Back) got his England break but possibly the surprise of their season defensively was Phil Jagielka - who did very well after coming in from Sheffield United.
For the future:
Already a key player Victor Anichebe is a very promising young striker - very effective as a substitute (especially in Europe this season).
James Vaughan is another highly thought of striker who has been at Everton since he was 9. He's only be a substitute in the league so far but was used in Everton's UEFA Cup campaign.
Lucas Jutkiewicz - another striker - English born but of Polish origin (and will play for them internationally apparently). Actually bought from Swindon Town in summer 07. Spent a brief spell on loan at Plymouth.
Jack Rodwell - highly-rated 17 year old Centre Back who made two substitute appearances for Everton in the Premier League this season - plus one against Alkmaar in the UEFA Cup.
Jose Baxter - England schoolboy international striker who is already a regular in Everton's U18s and was promoted to the reserves towards the end of the season.
Statistically Lewis Codling (12 goals for the U18s) and Kieran Agard (11 goals for the U18s & 3 for the reserves) have been doing well - but other than those stats I know little more about them.