NEW YORK (CNN/Money) - Yahoo! Inc. Monday said it will begin working directly with four companies specializing in "rich media" Web advertising technologies, such as those that pop-up in a new window, as the Internet media company seeks to bolster its flagging online advertising business.

Yahoo! said it will work directly with Eyeblaster, EyeWonder, Point.Roll and Unicast to incorporate their technologies into the online advertising packages it offers on the Yahoo! network.

Each of the four companies specializes in technologies that make it difficult for Web surfers to ignore advertisements.

Eyeblaster specializes in creating animated pop-up ads. Point.Roll's technology causes smaller ads to expand within the Web page on which they are placed when a user moves the mouse cursor over them.

For their part, EyeWonder and Unicast specialize in a technology that enables advertisers to deliver streaming audio and video messages into a Web page, similar to television commercials.

Yahoo! did not disclose the financial terms of its agreements with these companies, but they are part of a broader effort under way at the Sunnyvale, Calif.-based company to help boost its flagging online advertising business. As have most of its competitors, Yahoo! has been stung by a sharp slowdown in online advertising spending for more than a year.

Although the company has been moving to diversify its revenue stream, online advertising sales still account for the bulk of its revenue. When the company released its second-quarter earnings results week, Yahoo! reported a 4 percent year-over-year decline in online advertising sales.

Shares of Yahoo! (YHOO: Research, Estimates) were trading modestly lower on Nasdaq early Monday afternoon.