Primarily, there are two types of Sitempes
1. XML sitemap which is created for SE so that they can crawl and index every URI.
2. HTML sitemap which is created for the visitor so that they may know the structure of the website and can findout proper location of what they want.
Apart from this, there is one more type of sitemap i.e ROR sitemap. So, far as I know only big giants can render this type of sitemap.