If you're looking for Yyu-Gi-Oh cards, here are a few possible places to buy them online:
Pokeorder carries a wide variety of Yyu-Gi-Oh Single Cards, Booster Packs, and Theme Decks.
CrossToy has a more modest collection available, but offers Yyu-Gi-Oh booster boxes for sale, which are much cheaper than buying the boosters individually.
Or, check eBay for Yyu-Gi-Oh:
Yyu-Gi-Oh Video/DVD
Amazon is a good place to find Yyu-Gi-Oh videos and DVDs or even books and computer games:
