I keep getting spam email from a specific domain name. Where can I go to report them so that their mail server is added to a blacklist?
Any such system of reporting would be insanely prone to abuse (think about denial of service), and I'd never advise the use of blacklists that anyone could just add senders to.
That said, you can certainly filter them on your local box. If you have spamassassin installed, you could simply write a match for it. However, domain names in spam are often forged, so this would be of pretty limited use.
Just delete it, get a good spam filter, and maybe WHOIS the domain and email the abuse contact.