What to do with a pagerank 6 website?

1. Sell it. If you have large user-base you could sell your website for over $50.000, possibly going all the way up to a million.
2. Sell links on it. You could sell link places on your site. With a pagerank 6 website you should be earning $150 plus monthly per link.
3. Put different ads on it. You shouldn't put just the standard text ads, you should look for different ways to increase revenue. So you could put text link ads, banner ads and interstitial ads.
4. You can also park the domain for money though this is not a good way to monetize. You should park it only if you don't have much traffic and for whatever reasons can't manage and update the site with fresh new content.