I’m not a big fan of free directories for SEO. One of the major issues is that it’s hard to find “free” directories that will actually accept your free link without demanding a reciprocal link or subtly hinting that it will take your link 5 years (minimum) to be accepted unless you opt in for their premium $20 service in which case it will take 24 hours.
The other issue is the value these dime a dozen, link-farmy directories actually provide. You could probably spend your time better writing a good guest blog post and getting one quality link from a blog in your industry.
That said, if you’ve run into writer’s block and want to submit to a few directories, to spread your eggs around the SEO baskets, try this list. These are the directories that I’ve submitted to and actually did accept and list our site for free, with no reciprocal link (even if they did have reciprocal or paid options). If you have issues with any of them, please let me know. I don’t want to keep them on the list if they’ve changed their approach.
The SEO King (a little pushy with advertising to buy text links after you submit the link, but just close the window and they won’t bother you any more)
Viesearch (they bombard you with email ads after you submit, so use a spare email for this one)