Many bloggers are earning revenue by writing reviews for advertisers. There are many companies bringing bloggers and advertisers together, the most famous one is payperpost, it is also the earliest company doing such business.
But the bad news is that Google began to punish blogs that selling reviews a few months agon. Really bad for bloggers. It means they will lose revenue generates from blog reviews. They have to use other kinds of advertising methods like adsense. But I think adsene is not a good choice for blogs that have low traffic.
Now I have a question, what will the fate of companyies like payperpost be since Google has begun to kill someone? I've no idea. But I think Google's behavior will result of nobody caring about PR anymore. You know no one can dominate the advertising industry, it should be shared by all the people all over the world.