It's not really clear what you're asking, but one thing that you certainly can do on your website is recommendation. On Amazon, you have book recommendations, on Facebook - frieds recommendation, on last.fm - song recommendations. So whatever your site is doing, I'm pretty sure there's something to recommend your users.
So if someone's visiting a site that you've installed, and you've got an app that you're recommending, then that's something that might be helping them choose your next book or get on your next list of people who have said “I've liked it.” I think that is one of the great things about the web today. If you're a site that has information, and you can recommend that information, then you can also be a platform for your users. So recommendations are the big idea. So is this something I could possibly do with my blog or some of my other sites? It just so happens that when I found these things, the first thing I wanted to do was check them out with the public. And the first thing I found was that these companies have made a lot of money! Like I said, I'll keep doing this research if people.