Whale brains weigh generally between 4000-7000 g, elephant brains around 4000-5000 g, dolphin brains around 1700 g, and human brains weigh between 1300-1700 g.
Of course, remember that variations in brain weight within a species are quite considerable.
神はイルカを餌としてつくったんだぞ/ バチカンにきいてみれ/ 2 Headed Cow Born in China http://www.weirdasianews.com/2007/03/14/2-headed-cow-born-in-china/ http://www.google.com/webhp?hl=en#q=calf+two+heads&hl=en&safe=off&sa=X&tbs=vid:1&tbo=u&ei=jAyvS6uLCY_s7AOZnu26Dw&oi=video_result_group&ct=title&resnum=4&ved=0CBoQqwQwAw&fp=bcdf8cbbf06dc4f