Big is Better

From The Wine Avenger comes different bottle sizes.

The magnum (two regular bottles) is the civilized size for Champagne. Wines tend to mature more gracefully in larger containers, and Champaigne even more so. And let's face it, if there are more than two of you, you'll need another bottle anyway (there are only four glasses in a bottle). You should know that half-bottles and splits, which tend to oxidize before they even leave France, are strictly for tourists and the palate-dead.
Bottle Sizes:

2 - Magnum
4 - Jeroboam
6 - Rehoboam
8 - Methuselah
12 - Salamanazar
16 - Balthazar
20 - Nebuchadnezzar

I have seen the Magnum and possibly the Jeroboam, but probably nothing bigger. I may have seen a Methuselah in Wine Spectator. What's the biggest size you have ever seen?