Innistrad contains many cards with this ability. Innistrad really is a great set! Some of the Flashback cards have a different mana type than the card they are found on. This is a very interesting twist because with a guild-based block (RTR) we now can place Feeling the Dread in an Azorious deck.
With Flashback you can get to play a card twice. With Snapcaster Mage, you get to use that ability for ALL cards in your graveyard, even the ones that do not have Flashback. It is no surprise that this one card is supremely useful.