This seems to be address used by 50BTC since April this year

http://blockchain.info/address/1JVQw1siukrxGFTZykXFDtcf6SExJVuTVE

and this is another temporary one, which was used on the 18th October

http://blockchain.info/address/121Tk3oKDU3GHWeCRnxguzeeM7Tm3XvUns

before they switched to the one posted before

http://blockchain.info/address/198i5jrY1B4xGnQwbiDVuQzcq17thzaH1s


Here are some older pool addresses since August 2012:

April 2013 to October 2013: http://blockchain.info/address/1JVQw1siukrxGFTZykXFDtcf6SExJVuTVE
December 2012 to April 2013: http://blockchain.info/address/145UHBQAmGRpdsXVKhdHtFndnJ8XN8fLjq
October 2012 to December 2012: http://blockchain.info/address/151z2eoe2D9f6cohGNNU96GsKAqLfYP8mN
August 2012 to October 2012: http://blockchain.info/address/13XgASZP7N6pTMeyS5Sq8JeuCAkNzefnT7