When you first start planning your website one of your first considerations should be to make sure that your carefully crafted pages can in fact be found and read by those whom you target your page to. You need to use a two-pronged attack, first to ensure that the search engine spiders can find and index your pages and that they rank them well so the searchers will have the opportunity to see them.
Next, you have to ensure that once the visitor arrives at your site that he can easily find all the information you have provided. The three-click rule says that if a searcher cannot find the information he is looking for within three clicks he may just move elsewhere to see if he can find it more easily, This is the role of the navigation system that you should implement for your site. Let's look at each of them a bit.
Spider friendly menus and Site Maps
If your site is small and easily navigated and has say twenty pages or less you may find that a simple listing of page topics hyperlinked to the pages will suffice but if your site has many more pages than this it will quickly start to become difficult for users to search through them, though spiders will not generally have a problem.
We use and recommend DHTML menus which work by using CSS to control the visibility of layers. As can be seen above it is easy to put fifty or more links on such a menu without cluttering up the page. An added advantage of this type of menu is that the spiders can read them.
Site Maps for spiders and humans
If you implement a menu system that can be read by spiders you may not need a site map, but it does not hurt either. A sitemap should be made to do double duty so that it also helps your rankings a bit. I suggest using each individual page title as the visible listing and hyperlinking that to the correct page. There needs to be only one link to a site map preferably from the home page.
There are some very helpful tools to assist you in building menus and site maps.
Projectseven has both free Dreamweaver extensions to build menus as well as a very fast and easy menu builder.
The free Xenu Link Sleuth will spider the pages of your site, tell you if you have any broken links or orphaned pages and will build you a site map of the pages it finds.
XML new sitemap feature will help you to get a sitemap set up on your site and spidered by Googlebot.