As of April 2007 US/Canada border crossing regulations require a passport if you are traveling by air;
or two pieces of identification (birth certificate and drivers license) if driving.

Here are the links from both the US Government and the Canadian Government on US/Canada border crossing.
We will update them on a regular basis as necessary.

US Government
Canadian Government

April.01.2007 Posters are now avaliable for printing. To download, please visit our Publications section.

April.10.2007 Mail in registration forms can be printed for US, UK, or Canadian registration. Hopefully this will make the process or non-online submision easier.