Currently I am optimizing the URL's on my site for SEO and wondering what is the "best" way to structure an optimized URL. I have seen several different ways such as below and I am curious which is the way search engines like the most.

http://www.website.com/category/name-of-page/
http://www.website.com/category/name_of_page/
http://www.website.com/category/name-of-page.aspx
http://www.website.com/category/name...3/default.aspx
http://www.website.com/category/name-of-page/23/
http://www.website.com/name-of-page
http://www.website.com/name-of-page.aspx

Any ideas/views?