Submit your URL to these locations:
Submit url to Google
Most important search engine, will get your url cached in less than 24 hours. Most users use Google for web search so it is important to get listed here.
Submit your URL to Yahoo
Requires a valid yahoo user account in order to submit a link.
Submit by AddMe
They will submit your URL to 14 major search engines for free.
Submit your URL to Microsoft MSN search
Submits your url to Microsoft's search engine (MSN). This is the search engine that is used by default in Windows computers so many users will use this one.
More details
Most search engines like Google will find your site even if you do not manually submit it to them; if there are other sites that contain links pointing to your site then search engines will find your site thrugh those links. However not all search engines work like that and it is recommended that you manually submit your site, once every 6 months should be ok.
Other Submission Services
When trying to get your web site listed in many search engines you might also consider paying for a service that will do the submission for you, have a look at Godaddy's Traffic Blazer, it will submit your site to many important search engines and directories for $30/year.