The Major Directories

1. The Free Major Search Engines
2. Pay-Per-Click Search Engines
3. The Major Directories
4. Word of Mouth
5. E-zines -- market via your own opt-in newsletters

Directories are a different beast from Search Engines. They do not spider pages. Humans review and decide what gets in, think of them as gigantic bookmark lists, organized into categories and sub-categories, and sub-sub-categories, etc.

Here are the directories, in order of importance

Yahoo!

Still the grand-daddy of directories. Want to list in the Shopping and Services or Business to Business areas of Yahoo!? You must use Yahoo!’s USD$299 “Business Express” service ($600 for adult sites).

However, if your site fits in other areas of the Yahoo.com site (ex., noncommercial hobby or educational content) or in regional commercial areas at Yahoo!’s non-US English-language editions, you can still submit for free. At $299, you’ll have to decide whether it’s worth it. 
More info on the paid service
For instructions on how to submit
 

And for a low-cost alternative for entry into Yahoo!. Yahoo! has partnered with Overture and now displays up to 5 listings from this engine on its results pages. If Yahoo!’s annual recurring $299 listing fee is a little much for you, simply bid on a top 5 position for your most important keywords at Overture. While you’ll build far more traffic through the free and Pay-Per-Click Search Engines, a Yahoo! listing will bring you some traffic. And it will help in your link popularity score. Just make sure your site’s in top shape, with at least 20 good pages, before you submit.

Open Directory
http://www.dmoz.org/add.html
 http://dmoz.org/guidelines.html
 

LookSmart
You must pay to be evaluated, $299 if you want your site to be reviewed (not necessarily included, though) within 48 hours, $149 to be evaluated within 8 weeks. For the Express package, you can submit 5 URLs. LookSmart is gaining in popularity, powering more and more portals.

PAY FOR PERFORMANCE: 
LookListings targets medium to large businesses.. Subscribers select and purchase certain keywords and LookSmart displays these search results first in response to specific search queries, under the name Featured Listings. It’s expensive and not really an option for the small business netrepreneur. 
For more info
Its more affordable option is known as Site Promote

Ask Jeeves
Good old Jeeves is a bit harder to categorize. But, after you strip away the question-asking interface, it’s closest to being a directory. Ask Jeeves answers questions. Send an e-mail to url@ask.com, telling them which question that your Web page answers. For example, your Web page explains how to price a product, then tell the Ask Jeeves editor that your page answers How do I price a product?, include the URL.

Automatic Directories
You are automatically listed in the following directories when you submit to another one, as shown here

• AOL Search 

you are listed automatically in AOL’s directory when you submit to Open Directory.
• MSN Search 

you are listed automatically in MSN’s directory when you submit to LookSmart.
• Netscape Search 

you are listed automatically in Netscape’s directory when you submit to Open Directory.

Most services still maintain a free submit service, but there are benefits to forking out a few dollars

1. Fast inclusion into the SE’s index. Often you'll find yourself waiting up to 2 months after your site has been crawled before it makes it into the index. Paying for inclusion means you should see your site included within a couple of days.
2. Repeated, regular spiderings. Page-tweaking efforts are noticeable in a matter of a couple of days, no waiting around for weeks for a spider to re-index your page, and display those changes in the SE’s listing results.
3. Guaranteed continuous inclusion. Search Engines are pretty mysterious creatures. One day, your site will be sitting pretty with a top 20 ranking, and the next day it’s gone, disappeared without a trace. Sometimes the SEs cull pages from their respective indices for no discernible reason. Paying for your listing means it will never be dropped from the index.

Inktomi has implemented a pay-per-inclusion model called, Search Submit, that you may wish to consider. Payment guarantees 12 month inclusion in the index, as well as regular re-spiderings every 48 hours. Inktomi is now in the process of implementing click-through reporting on all its search partners’ sites. This allows subscribers to track the performance of each page within the program. As well, subscribers will be able to swap URLs slotted for inclusion into the program at any time Previously, not all of Inktomi’s partners offered this option. A powerful feature, this allows you to isolate and pay only to have your highest-performing pages listed in the index.

Pricing details vary depending on which partner you decide to subscribe to.
Position Technologies
VeriSign/Network Solutions

AltaVista’s paid inclusion service is very similar to the one offered by Inktomi. Unfortunately, AltaVista’s service is substantially more expensive than Inktomi’s and its prices are good for a 6-month subscription period.

AltaVista has partnered with InfoSpider to provide this service. 
Subscribe

Google offers an advertising option, the Google AdWords program.

Fast, with its crawler-based paid inclusion program called Fast PartnerSite, allows subscribers to track and measure their result.

Lycos also has a paid inclusion program. Lycos is really only a re-seller for Fast (Fast’s engine powers Lycos). 

Want a summary of the pay for listing/placement programs that are available? Danny Sullivan maintains a great page of all paid services offered by engines and directories. 
See SearchEngineWatch

Bottom line for all Pay For Listing / Placement services.

Stick to Pay-Per-Click offerings that bring you targeted customers. This yields measurable results. Kill programs with poor results, in the same way as outlined above in the discussions about what makes financial sense at Overture.

The best thing about the Pay-Per-Clicks is that they are guaranteed, targeted and cheap traffic. The free bargain if you can figure them out, some people will do better at it than others. But the Pay-Per-Clicks are guaranteed traffic. Site Build It! Manager makes the research and mass-submissions a snap.

And the directories are the same. If you build a good site that delivers high value content, you’ll get into the directories. After all, that’s exactly what they’re looking for, good sites that offer excellent content.