2 or 3 class configuration and an "Economy-Plus" configuration basicly differ by the level of service. In most airlines, the Economy-Plus" is just wider seats, extra legroom and extra amenities such as laptop power and larger personal video screen, but same level of service as in coach (same food basicly).
Airlines that offer a B-F united class (BusinessFirst in Continental, BusinessElite in Delta, TransWorldOne in TWA) usualy will not offer full flat beds as in First class but will offer extra amenities than the usual Business class of a 3-class airline.