There are three companies tech watchers are keeping tabs on, according to Crain’s New York Business. They have solid business models and could break away from the pack to become market leaders. Plus their revenues are in the millions. Chelsea-based startup ComiXology created a digital marketplace for comic books. In 2011, about 100 million comic books were downloaded from their site and sales revenue hit $19 million. They haven’t disclosed 2012 revenues yet, but the company expects it to triple. Medialet created a platform to buy and sell advertising space. It recently won a contract as the mobile ad server for Publicis Groupe’s Vivaki division. While not yet profitable, their revenue (estimated as eight figures) doubled last year and is expected to double again. Kaltura already has about 150,000 customers, including HBO, Cornell University and Paramount Pictures. Its open source media platform brings video to virtually any device. They are on the brink of profitability, with revenue somewhere between $25 and $50 million. Last year, they opened an office in Europe. This year: Asia.