I don't recommend using an "old fashioned" sitemap if you've got more than 20 pages on your site. The sitemap page, if you must have one, should be created for the user, not the search engines. Don't expect them to help your rankings.

If you've got thousands or even a few hundred pages on your site, then I would use a sitemap at all. If the users come across your sitemap "pages" they'll be confused and frustrated--and won't be able to find what they're looking for if they have to look at a huge list of links.

Pages with tons of outgoing links on the page are pretty much worthless when it comes to rankings because PageRank isn't passed (or if it is, not much is passed), and there isn't much link credit being passed. So, for ranking purposes, don't count on a sitemap helping you out.

It's much much better to rely on a breadcrumb trail type of navigation throughout your site. Break your site up into categories and make your main page link to your category pages--then your category pages should link to your other pages. PageRank and link credit will be passed, and if you keep your links categorized it will help with things like Google LocalRank.

It's better to have more incoming links to a page than outgoing links on that page. So, if you have 10 outgoing links on a page then there should be more than 10 incoming links to that page. A sitemap page with a lot of links on it will be pretty much useless if there's too many outgoing links on that page (by outgoing links I mean any link to another page, internal or otherwise).

Sitemaps and XML files, mainly made for the Google Sitemaps program are pretty much useless for ranking purposes. Sure, you will give Google a list of URLs to include in their index. And Google will crawl those pages. But if you only give the URL to Google and don't rely on PageRank being passed properly throughout your site via the internal linking structure then your pages won't rank well in the search engines. Don't expect to give Google a URL to crawl and expect it to rank anywhere for anything if you don't have everything else in place (like on-topic links to the URL). So, why waste your time creating a sitemap/XML file if you can get the pages crawled normally without a sitemap? They'll have a much better chance to get good rankings if you don't rely on a sitemap/XML file.

Huge sites like Amazon traditionally don't have huge sitemap pages--they have links to their pages from other internal pages on their site. Personally, I don't like to rely on sitemap pages or XML feeds to get sites crawled--there are other ways to get pages crawled and they might even rank well.