According to Euromonitor, by 2020, China and Russia will have displaced USA and Germany respectively in the top five global economies. For more details, see Euromonitor's blog.
Other recent postings to Euromonitor's blog include a video on the rising importance of sub-Saharan Africa, a posting on what opportunities does Africa's rising middle class provide? and a graph of the BRIC's move towards higher paid employment in 2012.