On my west coast offense teams, I usually have a big receiver [ala Raymond Berry or Jerry Rice] who excels at getting yards after the catch. Great route runners [Route God], great at getting downfield [Breakaway Burst, Strength Bonus and/or Quick Feet] and great hands [Soft Hands]. Tough over the Middle is a bonus as well!
One other thing: Do not underestimate the value of a receiving TE in a WCO!
IMO, receivers that fit WCO:
Raymond Berry
Jerry Rice
Andre Reed
Don Maynard
Dante Lavelli
Irving Fryar
Dwight Clark
John Taylor