I found a directory of directories called The Strongest Links that lists each sites Alexa rank, page rank, and accepted submission type (free of paid) offered. There’s also an “Info” link next to each listing where you can view the Alexa traffic chart for the specific directory and read more about the submission process.
The page can be sorted so you can start submitting to directories based on what is most important to you. It doesn’t really matter to me because I feel every little bit of exposure helps, but I did start with the heavy hitters first. I simply went down the list and added this site (and a few others) to all the ones offering free submissions.
A few of the sites caught my eye because they offered a little bit more exposure for your website by either placing your link in more places or higher in the results if you are willing to reciprocate with their link on your own site. A couple of them had some pretty decent ranking numbers, so I might have to go back over the list of ones I highlighted and take them up on the offer.
This list is pretty long and even submitting to just the free ones will take you plenty of time. However, if you’re feeling motivated and want to also weed through the some niche specific directories as well, they have a separate page for them located here. From just a quick glance, I see location based directories for different countries, service and retail oriented directories, and plenty just based on other interests. It’s definitely worth browsing through the list to see if any of them match up to your primary website topic.