I would like to put in a request for adding the ability to put top level domains in my blacklist (or whitelist, I suppose). Given that the only email I receive from certain TLDs (*.cn, *.gr, *.fr, for instance) is either spam or viruses, being able to target those domains in the email/antispam products would save me a lot of the time I currently spend in my email program, searching for everything from those T LDs so I can mark them for my junk filter.
You can already do so in the settings of the spam filter.
If this regards your Gmail account, there is also several filter options in Gmail