The new and improved Blizzard store opened recently, and it's definitely worth a look. It has a very clean layout, making finding what you want pretty simple. They carry everything from the Blizzard games to the Warcraft action figures to WoW game time. Their apparel selection isn't very large due to that primarily being handled by Jinx, but the store is still worthwhile.
Plus, registering for the Blizzard store comes with another perk. You can register for the Beta Test lottery, which is a chance at being chosen for upcoming beta phases of various games. Wrath? Starcraft II perhaps? All of the above? Who knows! I've been considering getting into the WoW TCG, so if I get a shot at a beta test out of it, too... hey, why not?
Edit: The Blizzard EU store is not yet live, but I imagine it will be soon. Sorry, Europe!