As far as the trailing slash, I answer that at the end of this post:
http://www.casinoaffiliateprograms.com/bb/no-link-url-text-question.12114.html?
It is not necessary for domain access, but files within a domain should be addressed with the trailing slash. In my opinion, I think it is good form to use it for domain names as well.
Reguarding the use of www to link to your domain:
http://www.stackedpoker.co.uk is a valid hostname
stackedpoker.co.uk is a valid hostname
Testing xxwww.stackedpoker.co.ukxx for HTTP access
Port 80 access successful
Testing xxwww.stackedpoker.co.uk for redirect to stackedpoker.co.uk
xxwww.stackedpoker.co.uk does not redirect to stackedpoker.co.uk.
Testing stackedpoker.co.uk for HTTP access
Port 80 access successful
Testing stackedpoker.co.uk for redirect to xxwww.stackedpoker.co.uk.
stackedpoker.co.uk does not redirect to xxwww.stackedpoker.co.uk.
No redirection detected… testing to see if stackedpoker.co.uk matches xxwww.stackedpoker.co.uk.
stackedpoker.co.uk HTML matches xxwww.stackedpoker.co.uk
According to the way you have your web server configured, or how your ISP has it configured, neither redirects to another. Meaning that xxwww.stackedpoker.co.uk and stackedpoker.co.uk displays the same exact index page. This means that either way is appropriate for displaying links to your site.
http:// should be included in all links, this is the correct way to formulate a hyperlink.
As far as SEO goes, I feel that the use of web standards and proper structure is very important. This is an opinion however, because nobody knows for sure. So lets see what others on here have to say…