In October Yahoo! picked up a 20% stake in advertising company Right Media. Today, Yahoo! bought the other 80% for $680 million in cash and stock.

This comes just weeks after Google picked up advertising giant DoubleClick for $3.1 billion. In other words, the big search portals ain't just about searching no more. Okay, that's been true for a while, but this makes Google and Yahoo! two of the biggest names in online advertising.

Right Media runs an advertising marketplace, or an exchange where advertisers and publishers can buy and sell online ads through auctions. Yahoo! had been using Right Media to place ads on its own sites since last year.

DoubleClick plans its own advertising marketplace, but has yet to do so.