I mostly use:
domain.com/some-random-page.html
domain.com/some-random-page/random-subpage.html
I can't honestly tell much difference between having the extension there or not though, the sites I have with an extension do just as well as the ones without one.
SEO wise I agree, just need to make sure you don't create any bot traps with your URL structures and it's all much of a muchness.
I like pretty URLs and they are good for security reasons so I normally use routing to strip server side technology extensions, ID numbers, non alphanumerical characters and then format URLs like: