Has a commercial airliner ever crash-landed in an ocean?
Yes, commercial airplanes have landed or crash landed in water many times.

If I am not mistaken, you are asking about scenarios when the on-board life jackets and life raft are used.

Here is a list of water landings. Examples when a life raft was used are (in addition to ratchet freak's mentions):


  On 22 October 1962, a Northwest Airlines DC-7C with 7 crew and 95
  passengers made a successful water landing in Sitka Sound. ... The
  plane stayed afloat for 24 minutes after coming to rest in the water,
  giving the occupants ample time to evacuate into life-rafts.
  
  In 1993, China Airlines Flight 605, a Boeing 747–409, ended up in
  water after it overran runway 13 ... All of the 396 occupants donned
  life-vests, boarded the eight slide/rafts and no fatalities resulted.