I rather like light colored tops with sheer lace bras. they do a great job of showing off a woman's breasts and what color her nipples are, with dark brown nipples against pale white skin working best.
Another way I enjoy showing her off in public is in a short dress / skirt with sheer mesh panties. Now that she has a small bush on top, it shows up wonderfully thru the mesh and gives strangers a great show when she is sitting.
With anything, you have to choose the exposure level to match the people you will be around. When kids are likely to be around, I just ask her to wear something cleavage revealing as opposed to being obvious with exposed crotch or seeing her nipples. She appreciated it and is willing to wear the revealing stuff when I ask, because I dont try to embarass her too badly