Part 1, Getting Indexed. Below is my take on what the average owner of a new web site needs to know about getting one's web site indexed by the search engines.
Google and Yahoo. Get used to it, these two are the mother load. Together they account for 75%+ of all search engine traffic. The next two (MSN and Ask.com) together account for 15%. After that, it's dribbles of traffic. Here is where you can submit your URL to Google and submit to Yahoo.
Search Engine Webmaster Tools. Both Google and Yahoo have webmaster tools that assist a webmaster to interact with the search engine. I find them useful for two reasons: (a) there is a process by which the search engine verifies your site and (b) the webmaster can request the search engine robot to come crawl his or her site for newly added content. Here are the links for Google webmaster tools and Yahoo webmaster tools. Yahoo calls it's version of webmaster tools "Site Explorer" and here is a link to more info on how it works. Google has a Webmaster Help Center that I have found to be useful.
Sitemaps. Through their webmaster tools, both Google and Yahoo allow for submission of specially coded .xml sitemaps. Why do it? Both Google and Yahoo index all pages contained within a sitemap submitted from a verified web site. Information from Google about sitemaps. Basically, a sitemap is a list of the URLs for all pages within your site plus a rank of importance assigned to page. Here is an explanation of the coding protocol to be used when creating your sitemap. Here is a sample sitemap and another sample. My recommendation is to use the .xml extension (although Google FAQs talk about .gz as well). The sitemap file goes in the root extension where your web site is located on the server (i.e., within the same folder as your web site's home page).
RSS Feed. RSS stands for Real Simple Syndication. It was created to syndicate news and blogs but can be used to alter to new content on your web site. They are created as XML files similar to sitemaps but created using a slightly different coding protocol, RSS 1.0. If your site is one that frequently puts up new pages, I recommend creation of both an XML sitemap and an XML RSS feed. The sitemap documents for the search engine all pages within the site. The RSS feed highlights new pages. Here is a link to the MedLawPlus.com® RSS feed.
Other Search Engines. Neither Ask.com nor Aol.com have a method for web sites to submit its URL for inclusion. Your site gets indexed by having inbound links from another web site which is indexed. Submission is made to MSN.com here. Below are additional, smaller search engines that take free URL submissions: