It's about $50,000 per academic year, so a total of $200,000 over 4 years. Many qualify for financial aid, so they won't pay as much (i.e., those who make under $60,000 don't have to pay for anything...
Tuition alone is $36,410 for 2008-2009, but I think with room and meal plan and various other things that you have no choice but to pay for its barely under $45,000.
For the 2007/08 Academic Year
Tuition - $34,530
Room and Board - $10,470
Books, Personal Expenses, Travel - $3,300
Total Cost = Approximately $48,300
Yale does offer need-based financial aid.