I also work with regional and city directories. These are very important if you want to draw customers just from your own part of the world. I find WebRings related to your company and get you on them. It's an interesting alternative to webpages that are lists of related sites. I have a tool that does a double-layer of back searches and helps me evaluate which sites to target first.
Some clients benefit enormously from being mentioned in online discussion groups and forums.
I also watch for any mentions of your company's or your product's name. You'll want to know how you're being represented by others. These can mention your website address. That should give you an idea of what I can do when I go to bat for your website. I'm not nervous about giving away too much of my approach because knowing what to do is just part of it.