Best of the Web is one of the oldest and most trusted web directories, adding your website to the BOTW directory can add great SEO value and can help increase your search engine rankings, and also occasionally bring in direct traffic from the directory itself.
When adding your site you can enter the coupon code SAVE20 to take 20% off your order. The offer expires at the end of October so you will want to order before the end of this month.
Some other great directories you can look into are DMOZ and the Yahoo! directory. DMOZ is free to submit your site, but it can take a very long time to be approved. Yahoo! charges $299/year.