Sets released: Worldwake, Rise of the Eldrazi, Magic 2011, Scars of Mirrodin

Major stuff:

   - Emblems were introduced in Scars of Mirrodin.  They sit in the command
     zone and carry an ability.  They aren't permanents, and Emblem isn't
     a kind of card.  They're essentially a way to get an ability to last
     for the rest of the game with a convenient reminder somewhere in the
     game, rather than just having to remember.
   - The life total rules for two-headed giant got simplified so that cards
     that care about a player's life total just see the team life total
     directly.
   - The Magic 2011 update clarified the deathtouch rules; when assigning
     combat damage, the declared damage order is used but any amount of
     damage from a source with deathtouch counts as lethal damage, so the
     rest of the damage can be assigned further down the line.

Minor stuff:

   - Worldwake gives us multikicker.
   - Rise of the Eldrazi gives us annihilator and a range of colorless 
spells,
     and makes use of the tribal type again.  It comes with leveler 
creatures,
     rebound spells and totem armor.
   - Scars of Mirrodin brings metalcraft, proliferate and infect, and brings
     back the imprint mechanic.