This year, American will receive two new aircraft types: the B777-200IGW and the B737-800. The first B777 is expected next month and the first B737-800 will come later this year. I believe that the first 777's will be put on the Tokyo and Osaka flights out of DFW, if they put them on Europe it won't be before next year. And it would be only on flights to London, Paris or Frankfurt.
The 737-800's will be assigned on medium-haul domestic routes (like the 757), for example MIA-LGA, EWR-DFW or ORD-SEA. The 737-800's will replace the remaining 727's. The 727's will be around for five more years.