From Dr. Weil:

Tip: Getting Enough Calcium from Food?
Most women need between 1,000 and 1,500 mg of calcium per day while men should get no more than about 1,000 mg. While it is ideal to get as much calcium as you need from your diet, certain foods are better sources than others - and some foods, such as alcohol, fructose, caffeine, wheat bran, raw spinach, salt and tobacco actually interfere with calcium absorption.

So what are good sources of dietary calcium? Sardines are a great source: they have 350 mg of usable calcium per 3.75 ounce can. Collard greens offer up 225 mg per cup, and tofu clocks in at 250 mg per half-cup. Other high-calcium foods include sesame seeds, broccoli and molasses, as well as dairy products and foods that are fortified with calcium such as orange juice and soy milk. Vitamin D is necessary for your body to properly absorb and utilize calcium, so be sure to get 400-800 IUs daily. If you need to supplement, calcium citrate is the best form to use.