We can immediately guess at some of the most acidic foods. Citrus fruits and juices, tomatoes in their many culinary forms, anything pickled in vinegar, coffee, tea, wine--these foods are certainly acidic, but also a regular part of many a healthy diet. You don't need to avoid these foods altogether, but it's best to enjoy them as part of a meal or enjoy them sparingly. And balance out some of these high-acidity foods at mealtime with low-acidity choices like bananas, bread, and dairy products.
Other sources of damaging acids might surprise you. Studies have linked sodas, energy drinks, and sports drinks to higher levels of tooth erosion. The combination of citric acid, phosporic acid and or carbonation raises the acidity levels in the mouth. And because we tend to sip them all day long, it's like a continuing acid bath for our enamel. Water is always a healthy alternative for hydration, but if you do indulge in a soda or sports drink, rinse with water after drinking the beverage to dilute the acid concentration.