Google is buying DoubleClick for 3.1 billion dollars in cash. Microsoft had also been interested in buying Double Click but lost interest when the price rose above 2 billion dollars. Yahoo and AOL are reported to have also been interested.
It looks as if Google is determined to dominate advertising the same way it dominates search. Some are saying Google paid too much for DoubleClick, but this is something Google obviously wanted very badly.
Here are some articles with more details:
Google scoops up DoubleClick for $3.1 billion - Apr. 13, 2007
Google to buy DoubleClick for $3.1 bln
Macworld: News: Google to pay $3.1 billion for DoubleClick