There is a growing -- make that deafening -- buzz about building a business using the iPhone App Store. And one of the most buzzed about areas is video. Even before the recent introduction of the new iPhone -- the first iPhone model to record and upload video -- watching YouTube, TV shows, and even movies on the iPhone was popular. Now, video apps are taking off. "Video on the iPhone is going to be enormous," says Matt Murphy, partner at Kleiner Perkins Caufield & Byers and manager of the iFund, a $100 million fund set up specifically to invest in promising iPhone apps. Here's a look at four companies fielding some of the most promising and creative video apps: This company's original video messaging app broke ground in user-generated video on the iPhone. That app combined still photos with audio to make brief videos. Now, the company is set to update the app to take advantage of the new iPhone's ability to shoot and upload video clips. Users will be able to upload 12-second videos to the company's site. They will also be able to sync to their Twitter and Facebook accounts, sharing clips instantly with followers and friends.

City Slicker This appmaker released a self-guided video walking tour of its hometown, Charleston, South Carolina, in August 2008. The app costs $9.99 and has more than an hour of video on 20 points of interest in the city's historic district. Using GPS, it also alerts users when they are approaching a site on the tour. Apple has named the app a Staff Favorite. City Slicker has since partnered with a large travel guide company to create tours of London, Paris, and Rome and plans to soon release at least 10 more city tours.

Zumobi In March, three-year-old Zumobi launched the American Idol Season 8 Exclusive app, which delivered 77 original behind-the-scenes video clips of the show's 13 finalists. The app first sold for $1.99 and has since been reduced to 99 cents. Zumobi also offers free apps for NBC's Today show as well as MSNBC's The Rachel Maddow Show. App viewers can watch short clips from either of the shows as well as videos of Rachel Maddow mixing her favorite cocktails.

videoNEXT This $49.99 app allows users to view live video streams from security cameras. The app can be programmed to sound an iPhone alarm when it detects motion. To allow the user to pinpoint a security breach, it can play back specific moments of archived recordings. The app will also let users remotely point the camera in different directions. VideoNEXT's customers are heavily weighted toward the defense industry, but the app should also appeal to small businesses and homeowners. It works with most security systems.

THE LINE: Given the new iPhone's ability to record and quickly upload video, is well positioned to capture an early lead in the video-sharing race. "Whoever gets the experience right as the popular site to post real-time video will lead the phenomenon," says iFund's Murphy. City Slicker also holds promise. Given its high production values, its use of GPS, and its reasonable price, City Slicker could turn out to be not just one of the coolest apps around but also one with a great business model.