Most of the search engines now have some sort of Local Listings where your business can be listed for free. Some of them are listed below.
Google:
www.Local.Google.Com - Click on Help, and then look for instructions on how to get your business listed. You must have (or sign up for) a free Google account, and provide the correct street address, as Google will mail you a PIN to confirm your listing
Yahoo:
www.Local.Yahoo.Com - You must have a free Yahoo account, and listings take a while to appear in their system.
San Diego Bizmart:
www.SanDiegoBizmart.com - Free basic listings for San Diego businesses.
Merchant America:
www.MerchantAmerica.com - Free listing, must signup for an account.
Benefits of getting listed include driving customers to your site, having additional links to your site (thereby raising your PageRank), and general name recognition.