According to research conducted by ZenithOptimedia in 2010 over $64 Billion was spent in 2010 on online advertising. Over 64% of this revenue went to only five companies; Google, Yahoo!, Microsoft, Facebook, and AOL. You can see the graph below for the full breakdown showing the percentage that each controls.

With such a large percentage of the market being cornered by a small number of businesses where should smaller businesses be putting their online advertising budget? Marketing via social media seems to be a popular choice as businesses are starting to allocate more of their marketing budget in to this portion of online advertising. Facebook is already #4 on this list, how much and how quickly will they be taking over market share in online ad spending?