There is a directory (a catalog of links) for just about every topic. There are also a few mega-directories that try to list all the websites on the internet. These directories will often link to your site for free, although sometimes they require a reciprocal link.
Make sure your site is finished before submitting it—nobody wants to list your under construction page.
Two of the most important ones are the Yahoo Directory and the Open Directory Project. Neither require a reciprocal link, although Yahoo's listings are only free for non-commercial sites. Make sure you find the most appropriate category for your site, and prepare to wait quite some time for it to be approved.
To find niche directories, you will need to search for them. For instance, if you sell organic handmade soap, you could search for:
bath products directory
natural products directory
You can also try searching for words that are typically on a directory site:
handcrafted goods "add site"
handcrafted goods "submit site"
Avoid submitting your site to directories that don't relate to your business at all, such as free-for-all links pages. Search engines like links that are relevant to your site content.