Many internet gurus will tell you to build websites based on niche areas with high search volumes. If you are looking for something different, why not start a news site or blog (if there is any difference) on a particular industry. Most industries have some kind of trade magazine that all companies that belong to that industry subscribe to.
Most of those publications are pretty dry reading and are published about once a month. If you need an idea for a website, why not create a blog on that particular industry. You could spice it up a little with lots of industry gossip and news. I would probably restrict it to an industry in just one country or region. You aren’t going to get a huge amount of traffic, but it would be easy to become the online authority for that particular industry.
I imagine you would have to start with doing fairly boring news, but you could then start doing interviews with CEOs and key players in the industry. Most executives love seeing their name in print, so they will send interviews to all of their colleagues and friends. Eventually I think you would get people sending you anonymous tips, which you could then break news and regular business newspapers and magazines might pick up on. Of course, you would need to be careful not to publish anything defaming.
I doubt that Adsense or affiliate links would work. You would probably need to sell advertising directly like what magazines do. Since your costs would be much lower than a printed magazine, I think advertisers would see this as a good deal. Most executives have email and internet now, so I don’t think it would take too long to get recognized in the industry.
Adding a job board could be another source of revenue. Make friends with recruiters and I am should you could pick up on some great gossip.
The tech industry is already so well covered, I would target an industry that is traditionally not so tech savy. Hotel, airlines, mining are some ideas.