The best sources of lutein (and zeaxanthin, its close relative) are dark green leafy vegetables such as kale, spinach, turnip greens, collard greens and romaine lettuce.
Broccoli, zucchini, garden peas and brussels sprouts, corn, kiwi and honeydew are also good sources. Lutein is also found in the red, orange, and yellow pigments of fruits and vegetables; for example, tomatoes, carrots, and squash.
Egg yolks have the highest concentration of lutein and zeaxanthin among all foods high in lutein content. Although they contain significantly less than spinach, eggs are a much more bioavailable source of lutein, and consuming eggs increases levels in the blood many times more than spinach.
Cooking leafy green vegetables on low heat can increase the bioavailability of the lutein by breaking down the cell walls and the carotenoid-protein complexes.
For best absorption, eat all carotenoids with some fat. One of the pitfalls of a low-fat diet is that you won't absorb your carotenes very well, including lutein.
Here is a list of foods high in lutein content:
For prevention of degenerative eye problems, you can find supplements that combine lutein with other antioxidants beneficial for eye health. Refer to my page on Lutein Supplements to learn more.