One of the hardest things about natural linkbuilding is trying to build links to sites about escorts, viagra, loans and insurance. My favourite method is to think outside the box and try to set up clean versions of the site (or even seperate sites) so that people are happy to link to them.
For example to rank an escorts site highly you would create a site about Ford Escorts and become part of the car community exchanging links and writing useful articles to attract natural links. After a year or two you can redirect traffic to your real site and take advantage of the anchor text and links from trusted sites that your competitors can’t get.
Another idea is to build links to your loans site – create a site about something similar to loans such as a personal blog from the made up person JohnSloan.com the anchor text you will get has the word loan in it and should help your rankings when you 301 it to your loans website.
If you want to rank for an insurance term you start with a news site, write high quality news and once you get enough link equity 301 the site to a less news focused and more commercial domain name. Keep pushing out the news but make your front page more commercial.