One of the most important tools in maintaining your body's joints and increasing flexibility is a good supply of Omega Fatty Acids. I recommend either a *high quality* fish oil or, if you are vegetarian or otherwise fish-averse, a high quality flax seed oil.
Quality makes a big difference, especially with the fish oils. You want to consider the source, quality, freshness, potency, and purity of the oil and check to see if it is from a sustainable fishery.
Here is an article with more information than you ever thought you wanted to know on fish oil supplements: http://chriskresser.com/the-definitive-fish-oil-buyers-guide.
One spoonful of this elixir every day will keep your joints lubricated for healthy, happy bending!