5
You can always pay to improve your placement, but usually you can get into most search engines without spending cash.
Google will spider any links to your site, so including it in link databases like the one in xoops.org would help a lot.
Yahoo! will let you include your site in their directory for free if it's not commercial. If you have a commercial site, make a personal one linking to it and add it (personal) to yahoo!.
The greatest source of information for search engines lately is the Open Directory at dmoz.org, I guess. You can submit your site and have it listed in the right category for free.
Altavista, Lycos, Google, all will let you submit your site for free but with no guarantee of inclusion. Some smaller services, like aeiwi.com/, will add you right away.
All in all, best thing you can do to get good places in search engines is having interesting content. Choosing the right words for creating links (never "click here", "here", "this one", always something related to whatever the link points to) will help too. Getting people to link to your site is always good, specially if those people are somehow related to your site's subject. Never use link farms or banner exchanging programs, they are annoying and don't work well.
Good luck
