Today we lose some valuable members of the Standard metagame.
We bid farewell to Bloodbraid Elf; Sprouting Thrinax; Elspeth, Knight-Errant; Master of the Wild Hunt; Sphinx of the Steel Wind; and a host of others.
Today is the second Standard rotation since Wizards of the Coast changed up the way Core Sets and Standard/Extended format rotations would work.
Today in Standard, we lose 4 sets: Shards of Alara, Conflux, Alara Reborn, and Magic 2010 Core Set.
In their place, we picked up Scars of Mirrodin since it released today.
Extended lost a lot more. Extended loses Teferi, Mage of Zhalfir; Venser, Shaper-Savant; Tarmogoyf; Wrath of God; Damnation; and more.
Extended rotates at the same time Standard does and only keeps the last 4 years' worth of expansions and a few Core Sets. Therefore, rotating out with Scars of Mirrodin's release are Time Spiral, Planar Chaos, Future Sight, and 10th Edition.
To catch you up on the current Extended list, here are the permitted blocks and Core Sets:
Lorwyn mega-block (Lorwyn, Morningtide, Shadowmoor, and Eventide)
Shards of Alara block (Shards of Alara, Conflux, and Alara Reborn)
Zendikar block (Zendikar, Worldwake, and Rise of the Eldrazi)
Scars of Mirrodin block (currently only Scars of Mirrodin)
Extended format rotates once a year now, at the same time as Standard, and is looses the oldest block (out of a 4-year list). I'm not sure how the Core Set rotation goes, but if it's like Standard M10 will tie in with Zendikar block and won't rotate out for a while.
Be sure to update your decks if you're playing these formats! I'd hate for you to end up DQ'd because you've got the wrong Elspeth in your deck.