These are the foods I eat on a daily basis with highest magnesium intake:
Mixed Nuts - 308 mg per cup
Spinach - 150mg per cup
Yerba Mate - 90mg per cup
Chocolate Soymilk - 39mg per cup
Coffee (espresso) - 96mg per 4 oz
Total magnesium: 683mg
Luckily I'm meeting my recommended intake of 400mg per day.
Check your intake here: http://www.nal.usda.gov/fnic/foodcomp/search/