There are a couple of more checkers as well as Bobby.

Take a look at the following URL.  Pay particular attention
to TOM.  Not only will it check a page, it will send you
back a page that will be accessible.

I don't have time now to give details and I am going from
memory so, I might have the info a bit mixed up.

Towards the bottom of this url you will find

TOM
Dr. HTML
and
BOBBY

http://www.rit.edu/~easi/access.html

Dick