I hesitated on posting this early in the day, namely because when I think of Zazzle, I think of indie people producing their own merchandise, and not a place for official merchandise, but it seems MLP has its own Zazzle account. Unlike Hot Topic / WeLoveFine, these are more mainstream to the show, what I would call ‘classic’ t-shirts. Several examples are above, pretty straight forward artwork but some enjoyable designs. Being that it is Zazzle you can get these in various forms (I think I even saw hoodies), and ranging from kid size to adult male & female. There are also 3 ring binders, and one section which you can have your name or a message printed out along with the picture.
Also if you are into the “classic” MLP, they also have their own section.