I've always found it's best if it's stored in your stomach but 5 mintues of google searching and I came up with this:
"All wines keep best in a cool, dark place with consistent temperatures around 55°F. Fluctuations of hot and cold can ruin a nice bottle of bubbly, and chilly extremes are just as harmful as high temperatures.
Don't keep a bottle of champagne chilled in the refrigerator indefinitely, waiting for a reason to celebrate -- by the time you pop the cork, it may not taste very festive. An article on storing wine from About.com recommends refrigerating champagne for no more than a couple of days. Return it to the somewhat warmer conditions of your wine cellar for longer term storage. If, like us, you don't have a wine cellar, the FAQ at Wine.com suggests that 45°F is the optimal temperature for both serving and storage. "
http://ask.yahoo.com/ask/20020124.html