Sasaku
Like I have posted several times before, because of my workout partner's job, he does an inordinate (freaky) amount of cardio. More than 99% of the population and can and has done even more than that. He uses a few supplements.
I'll mention a few. He will use Beverly International Muscle Provider Protein or Beverly International Mass Maker Protein instead of or in addition to meals.
He will use a creatine blend before a heavy cardio workout, such as MuscleTech Cell-TECH.
This is quite nifty DURING his extreme cardio workout, he will use a product called Clif-Shot. This is a terrific energy and complex carbohydrate gel that you can squeeze out while running.
I am not promoting any site, but you can find more information on Clif Shot here:
http://www.amazonsupplements.com/clif-shots.html
After the workout, he will use Cytomax, Endurox R4, and/or Optimum Nutrition AfterMax for recovery. These all work really well.