Directories are a key source for increasing backlinks, some directories charge a price for this service and others allow you to submit website links for free. All good free directories have the following characteristics, they review submissions and supply submission guidelines. Directories full of spam links isn’t going to be helpful to the directory or the websites listed in them. The on page SEO needs to be at a good standard and listings should be do follow. Page rank should be at a moderate level.
This directory has been around for a while and has kept there listings spam free for 10 years. You can get a quailty backlink here and there premuim listing doesn't cost an arm and a leg. Well mantianed unique directory.
The famous directory that is dmoz. This directory is wrothy of being number one of this list but it's not. Google uses this directory as a reference hence its popularity. Provides a quailty listing that actually provides a trickle of traffic and the poteneial of getting more backlinks due to other new directories copying dmoz categories and listings.
Very hard to get listed here, advice given to people trying to get added is to, submit and forget about it, it is only a directory afterall. Maybe over hyped but still one of the best.
Page rank isnt everything you know. I like this directory the template is unique and it is very neat and attractive to look at. Given time this will be popular and if you have a good website it has a better chance of being accepted here compared to other directoies on this list.