Pre-Constructed Magic decks are a great way to learn and also are an interesting historical record of how the game has evolved through the years and an insight into the mind of the official game designers at Wizards of the Coast.
We have a very comprehensive collection – complete Duel Decks and Planeswalker Decks – almost every preconstructed deck ever made! Commander decks have their own page here. We also have some very interesting decks made by MNC staff – but they’re not listed online.