Tops with self-belts or other belted tops can work well too as long as the belt does not fall below the natural waistline.
Although styling of the top is key, you can also use color contrast to bring out the waistline definition. When the waistline band is a darker color, the definition created is more pronounced and desirable. Dark colors recede, which makes the area covered by the dark color look smaller. Tops with curved-seamline, side panels in dark colors that contrast against the color of the front can also create the illusion of a waistline. These types of tops can be difficult to find, but if you sew, you should be able to find or design a workable pattern for such a top.
Avoid tops that have too much sleeve or detail unless you balance your look with details that add hip interest too. Otherwise, your naturally balanced figure can appear unbalanced.
For an evening look, try a corset-type top that cinches your midriff.
In the example above, the dark waistline band of the graphic print top from Petite Sophisticate (Vendor's Site) contrasts with the print and creates a defined waistline. The V-neckline, also emphasized by a dark band helps make the wearer look taller.