Macromedia Flash has quickly emerged as the dominant technology in the rich-media game for various reasons. For one thing, it offers good reach. The Flash Player comes preloaded on most new browsers, and Macromedia claims that 98.3 percent of all computers--some 414 million users--have the plug-in installed. What's more, Flash uses vector-based graphics to keep downloads palatable, streaming allows ads to begin playing before they're fully loaded, and Flash ads can incorporate sound and interactive components such as mouse-overs.

What about the 1.7 percent of machines that don't have the player? Most respected sites require developers to deploy sniffer code to detect the plug-in or lack thereof. If the player isn't installed, the ad server will simply default to a static banner or GIF that's animated by frames of the designer's choosing. This way, the user still sees an ad (albeit a less engaging one), and the page loads fully.

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s to keep downloads palatable, streaming allows ads to begin playing before they're fully loaded, and Flash ads can incorporate sound and interactive components such as mouse-overs.

What about the 1.7 percent of machines that don't have the player? Most respected sites require developers to deploy sniffer code to detect the plug-in or lack thereof. If the player isn't installed, the ad server will simply default to a static banner or GIF that's animated by frames of the designer's choosing. This way, the user still sees an ad (albeit a less engaging one), and the page loads fully.

Flash is by no means the only player in the game, however. San Fransisco-based ad agency Freestyle Interactive recently garnered three Clio Awards for its Hewlett-Packard Invent campaign. Using Java to power some elegantly simple yet standard 468x60 ads, Freestyle's designers invited users to manipulate elements within the banner. In one example, users can change the numbers in a mathematical equation and watch the effect those variables have on the color, frequency, and wavelength of the undulating graphic in the background.

The message behind the ad is admittedly subtle and provides scant motivation to click--the click-through rate for the campaign's 12-month run was only 0.4 percent. But according to Freestyle's case study, the effort was primarily concerned with branding. By that measure, or at least judging by the mesmerizing effect of the ad, it worked.