At the moment there is a lot of uncertainty about the advantages of directory submissions with regard to SEO i.e do follow backlinks.
My advice is that it does not take too long to submit to a handful of directories and it does not hurt your rankings so do it!
Also there is the possibility of getting human traffic from the directories to your site.
The directories listed below are free to submit to and also do not bombard you with unsolicited mail.
http://www.jayde.com/ One of my favorite. really good service
http://www.dmoz.org/ It'll take for ever if it happens, but said to be liked by the big G
http://freesubmit.thetam.net/ Very quick turn around
http://www.best-net-sites.com/ Another quick turn around
http://www.best-sites.co.uk/ Quick inclusion and email confirmation
http://www.somuch.com/ Another quick turn around with email confirmation
This is just a short list. But there are loads of directories out there you can submit your URL to. Just be careful that there are no hidden costs.
Till next time