Malaysia Airlines flight 17 en route from Amsterdam to Kuala Lumpur went down over Eastern Ukraine near the Russian border. Unconfirmed reports say that it was shot down by a surface-to-air missile.
Update: Ukraine says their forces were not involved. New information indicates that pro-Russian separatists were the ones who shot the plane down.
Update 2: This Facebook post from the boss of the pro-Russian separatists in the Donetsk region brags about shooting down an aircraft (Antonov AN-26) around the time that the Malaysian Airlines flight was shot down.