Navigation Menu SEO?

Keep the sitemap on every page. Usually google looks at "How easy it is for a visitor to reach a page".

Proper sitemap on the page is an essential part of SEO.

Formatting wise it's up to you, I'd just be careful about using javascript or image links unless you mean to mask your keywords or avoid spamming your main keywords.

Something I've noticed that helps is to have category-level keywords there and have a preferred landing page for every "category" level keyword that can link to your other posts on that topic.

If you have a dog training site, for instance, you don't want to clutter your main navigation with every longtail keyword post in your top navigation (or sidebar) - but for a user's perspective and an SEO perspective it helps if you target terms that are more broad rather than longtail in nature.

"leather jacket for cockapoo" would be a longtail keyword.

"dog clothing" would be more of a "category" that would be fine to link to - and for a user would make sense if you break your site down by category that they can navigate through to find what they need.

But I wouldn't use it for your super longtail keywords...think in terms of topic and user-friendliness, and going back to format, I'd suggest keeping it to text links (not sure that's what you're asking) and drop-down menus are fine.

It just need to be clean coded (on W3C standard) with right and keyword rich Title/ALT tags