Sunnyvale-based Yahoo! said today that it is in an agreement to acquired Right Media, an online advertising network, for $680M. The firm said that the cash and stock deal is an important step in its efforts to build its advertising and publisher ecosystem. Yahoo previously owned 20 percent of Right Media as part of a prior strategic investment in the firm made in October of 2006. The deal follows Google's $3.1B acquisition of competing online advertising firm DoubleClick earlier in the month.