The best sources for magnesium are wheat germ and bran, but you can get good sources from whole grain products, nuts, legumes and some leafy green vegetables.
All of these things are great for a healthy diet anyway, so you could start incorporating them into your meal plans.
Did you know that you can add things (like magnesium) to your Nutrition Tracker? Once you have this added, all the foods you track will have the breakdown that includes the magnesium levels. Adult females need 310 mg daily for ages 19-30, and 320 mg daily for ages older than 30.
There is some more information in this link - you'll have to scroll down the page til the Magnesium section: www.sparkpeople.com/resource/reference_min
To change your tracker to monitor your Magnesium, go in to your tracker. Above the little glass of water, there is a link there called "Change Nutrition Goals". Click on that link. When the page opens, scroll down a bit til you see the box called "Add Another Nutrient to Track". Choose Magnesium from the drop down list. Click on the orange box at the bottom of the page that says "Save your changes".
You can add as many things as you'd like from this page (fibre, salt, caffeine, etc).