Avoid anything refined. A good rule of thumb is anything that's "white" (sugar, flour, rice) is refined and to be avoided.
While you're pregnant, you need to maximize your nutrition. These refined items have very little nutritional value, even if the label claims they're "fortified." They also spike your blood sugar level and insulin levels, neither of which are a good idea during pregnancy.
If you eat a "real food" diet, you and your baby will be better off. Unprocessed meats, fresh (or frozen) fruits and veggies, whole grains like oatmeal, barley and stone-ground wheat. Obviously, don't deprive yourself. If you want a slice of cake, have it. But, speaking from experience, you'll need to temper the urge to eat the whole cake (and justifying it by saying "but hey, I'm pregnant!").
Also, please avoid artificial sweeteners. There's no conclusive evidence that they're harmful, but there is STRONG evidence that they increase weight gain even though they're non-caloric.