Just give them bogus information. I found that the washington post's registration page doesn't think it's possible for someone to be born before the year 1900. I figured the zip that they cite as an example worked. As for the 'sex' question, there was no button for 'yes', so I just randomly chose one. I feed all sites that ask for stuff like that random information, and then purge their cookies once I've read what I want to.
If there's one site that's sure to "purge my cookies" it's the Washington Post.