Journey to the Center of the Earth and its sequel Journey 2: Mysterious Island are probably the cream of the crop in terms live action 3D currently available on BluRay. Neither film will ever win any awards for plot or acting but you more than get your money's worth in terms of depth and 3D pop-out effects.
Yogi Bear is another one of those family movies that may make you cringe at times but also had really strong 3D and some nice effects.
Hugo is another good choice with excellent 3D imagery though the plot, which mixes melodrama with a celebration of the early days of film, might be boring for some.
Men in Black 3 is one of the better 3D post-conversions with nice depth and lots of pop-out effects in an entertaining and accessible movie.
Those would be my picks for accessible 3D family fare.