Editor's note: a number of these tools are changed or no longer available.

Google: How To Submit to Google Webmaster Tools

Submit your site to Google's search engine via Google Webmaster Tools

Find instructions at Using Webmaster Tools

Bing: How To Submit Your Website To Microsoft's Bing

Bing (was MSN Search) is Microsoft's new search engine service.  Their  WebCrawler, MSNbot, will index your site.

bing.com