Supplements

I've found it necessary to supplement my diet for a variety of reasons, though essentially it's because even the best diet cannot assure that you get everything that you need to function at an optimal level.

My basic supplement recommendations include:
Fish Oil - 4,000 mg/day. This has anti-inflammatory properties and really helps improve mental functions.
Fiber - 1,000 to 2,000 mg/day. Our diet is fairly low in insoluble fiber, so we supplement to avoid getting plugged up. Colon cancers are becoming a bit too common, so this is good insurance.
Vitamin D - 4,000 mg/day during times of the year when we don't get adequate sun exposure. During the summer there should be no need to supplement if you are getting 10 minutes of sun exposure around noon everyday. This supplement amount is based upon a recommendation by the Vitamin D Council. Visit their website to learn more about this important nutrient, as it has tremendous health consequence for everyone.

I take a couple of supplements specifically to improve a condition known as Raynaud's Syndrome. These were recommended on an alternative medicine site and while they haven't cured the disease, they seem to have improved my cold tolerance, allowing me to commute in relative comfort by bicycle at temperatures as low as 8 degrees Fahrenheit for a half hour at a time:
Taurine (an amino acid) - 1,000 mg/day
Magnesium - 250 mg /day
The Magnesium seems to have had the added benefit of greatly reducing the amount of cramping that I used to experience while doing intense exercise in high temperatures. Experts claim that the majority of Americans eat a magnesium deficient diet, so you may want to consider this inexpensive supplement.

And I take a supplement for joint and bursa pain and inflammation, rather than taking "Vitamin I" (ibuprofen, which has some very nasty long term side effects):
Triple Strength glucosamine/condroitin - 2 tablets/day (for joints). This really helps lubricate the joints, but you need to take if for several weeks at an adequate dose to notice any improvement.
In the past I've taken Borage Oil (2,600 mg/day) to also help with hip bursa pain. I wasn't convinced that it helped any more than Fish Oil.

A number of supplements are purported to help lower blood pressure, including Grape Seed , Turmeric and the amino acid L-citrulline. All of them seem to have helped to keep my blood pressure at excellent levels, though increasing my intake of fruits and vegetables has had a more profound effect. I currently only take Grape Seed (200 mg/day) and Turmeric (500 mg/day).

In my cycling and strength training I also use the following:
GABA (an amino acid, 3 g per workout), prior to intense workouts only. In conjunction with intense exercise it has been shown to increase the production of human growth hormone, but this has not been definitively proven. It's an inexpensive supplement, so while I can't know for certain that it works, it's worth risking a few dollars in the hope that it does. I did see very significant performance improvements the first year that I used it.
Alpha Lipoic Acid and Acetyl L-Carnitine (800 & 400 mg/day, respectively) for the purported benefit of increasing the number of mitochondria in your body, a particular problem for aging cyclists. I haven't used this enough to have an opinion of whether it works or how well it works and haven't seen the research that would back up this claim.

I attribute my ability to live relatively pain free and to generally avoid common illnesses to frequent intense exercise, my diet and the supplements that I take regularly. I can't say for certain that the ergogenic supplements that I take to improve my cycling performance are having the desired effect, but at the same time they are safe and relatively low cost supplements, so I find the risk to be worth the potential reward.