The ones that you generally can’t go wrong with is:

DMOZ – Free. Lists sites and relevant useful deep content. Listing may take a long time. Difficult to get listed in.
Yahoo! Directory – Pretty much all of my (commercial) websites are listed here. U.S. $299 review fee ($600 for adult) annual. If you’re lucky enough, some of the regional directories may even be free. Not the case in Australia though.
BOTW – Another site I use often for most of my websites. $69 recurring fee or $99 one-time. There’s also a sponsors program which lets you list text links in high category levels.

These are listed in the order I go through each time with a new site/client. DMOZ does have the option of allowing you to apply to become an editor. If you say you want to be an editor for SEO-related reasons, you won’t get accepted. If you say, however, that you want to help the web or something along those lines, it would help your application.