- Standard Nav - Outputs Current Page, it's children and all it's peers in a list/nested list. It automatically omits all top level items because the assumption is that you will have some sort of Primary Navigation and it would be redundant to include in two places. Since there's no way for us to know how deep any site is going to be and navigation quickly becomes unusable once it gets deeper than 3 levels, the standard nav is relative to where you are in the site. As a result, it works best to pair it with the Breadcrumb Navigation so the user knows where they are in relation to the homepage.
- Portal Nav - Same as Standard Nav but does not output any children of a portal. This is useful for "News" or "Press Release" portals where you might have a large number of children and would blow up your nav if you used the standard nav.
- Peer Nav - Exactly what it sounds like. Outputs links to all item on the same level that you are on.
- Sub Nav - Outputs links to any children of the Page you are on.
- Sequential Nav - Outputs a numbered sequential list of items that live in a portal. This useful for "tours" and such.
I think all the nav's ignore the root and the first level pages as stated in the Standard Nav. The Site Map works however.