The latest concept in online advertising is the video and audio ad units. Whilst still in its early stages, most bloggers can increase their blogging income by incorporating one of these ad units on their site.
I have my doubts as the long term value of audio ads in their current format. They do not have any user control and are generally played as soon as a page is loaded. This will have the effect of slowing the load speed of the page.
Video ad units on the other hand look to be a much better prospect. These load as static images and require the user to click to play. It takes a second click to visit the advertisers web site. Google are the latest to ad video ads to their ad unit inventory and come in a variety of sizes.
At present the number of advertisers using video ads is fairly low, however as the concept grows and the production costs fall and I can see many more advertisers adding the concept to their advertising programs.
Google have several articles relating to the concept that are well worth reading if you are looking to add other options to your blogging income portfolio.
