MediaBuyerPlanner: Outdoor is the second-fastest growing major ad medium, just after the internet, according to estimates from the Outdoor Advertising Association of America, with a growth rate of 11.4 percent in March, Mediapost writes. First quarter revenue grew 7.7 percent over the same quarter in 2005. The winter months typically see a dip in spending, which means that this summer could see even more growth, says Stephen Freitas, chief marketing officer of the OAAA.

New technology, including digital billboards, have been helping to drive the growth. Freitas said that he has heard from many an outdoor company that even before a digital sign is built, it's sold out more than a year in advance. Advertisers are also increasingly becoming interested in reaching consumers when they're on-the-go, particularly since consumers are spending more time out of their homes than any generation previously.