Just as the PR industry is beginning to figure out how to integrate bloggers into campaigns for their clients, new channels are emerging that may have even more potential than blogs – online TV. Thanks to the growing popularity of YouTube and other video sites, 15.5% of US households are now watching internet video compared to 9.4% who are buying and downloading music files. Across all age groups, watching internet video is significantly more popular than reading blogs. And in the over-25 crowd, it beats social networking as the primary online activity other than email.

A number of companies are taking advantage of this trend by launching online television networks. The March 19th edition of BusinessWeek notes that N3, Next New Networks, launched six channels in March on subjects from “sewing to comics.” Founded by veterans of MTV and AOL, the network hopes to launch 100 “super-niche” web channels.

Further along in its development, Diggnation attracts hundreds of thousands of viewers along with 15 corporate sponsors who pay $10,000 per episode, according to Business 2.0. For 45 minutes, the two 30-something hosts discuss the latest tech gadgets, often plugging their favorite products.

Another ready-to-launch web service called Joost has compiled 2,000 hours of copyright-protected programming to appeal to young males with content including extreme sports and shark videos. Michael Eisner’s latest venture, Veoh also plans to offer a niche series like Fearless Cooking, Triathlete TV and Wine Library TV.

Given the low cost of entry, we can expect to see hundreds of net TV offerings popping up in the next couple of years – all geared to highly-targeted audiences who are passionate about a specific topic. Imagine the opportunity for PR people when there are thousands of new broadcast outlets where they can place a product or a spokesperson. Compared to network TV, the viewership will be small but the potential will be enormous.