I have the exact same problem. I cannot access my website via http, but have no issues reaching it via ftp. I can access any other website on the net.
After spending many days accusing my web host and ISP of incompetence, the router proved to blame in every test.
My $110 linksys runs into issues, yet my $20 router doesn't... hmmmm?
This also happened to us at work a few weeks back. Same router same model! Work canned the linksys right away.
Hey Linksys... where's the fix?