What are flavonoids-and how much should I eat per day?

Flavonoids are colored pigments in a variety of foods and there are more than 4000 that have been identified. They are mostly known for their antioxidant, anti-inflammatory protection to cells which can protect the heart, circulation, blood, and brain as well as having cancer or anti tumor benefits.  There are no current recommendations for daily flavonoid intake at this time but some signs that you might not be getting enough flavonoids in your diet are: Frequent colds and infections, bruising easily, frequent nosebleeds, and excessive swelling after injury.  It is estimated that the average daily flavonoid intake in the US is about 150-200 mg which is certainly not adequate given the standard American Diet.  You can increase your daily intake of flavonoids very easily by eating a cup of blueberries or blackberries which contains over 400 mg of flavonoids, 1 cup of green tea can contain as much as 1000 mg, a small red apple with skin has around 200 mg, red onions, celery, and kale are also high in flavoniods. Check out the USDA's flavonoid content of foods database for flavoinoid content in foods.
Foods rich in flavonoids are fruits, vegetables, tea, and legumes. 
Common subclasses of Flavonoids are Anthocyanidins from grapes, Flavonols from teas, chocolate, apples and wine, Flavanones from citrus fruit and juices, Flavonols from yellow onions, kale, scallions, broccoli, apples, berries and tea, Flavones from parsely, thyme, celery and hot peppers, and Isoflavones found in soybeans, soyfoods, and legumes. 

Try to include 8 fruit and vegetables daily.  2 vegetables for every fruit, some green tea, and maybe a bit of 99% cocoa and you will be good to go!