Paul, there is no free PDF of the Reference Guide. You can download a free PDF of the rating system requirements—but that only consists of the credit language, not the implementation guidelines and other content included in the LEED Reference Guide. It is generally recommended that you make the leap and buy it—there is content you can't get anywhere else, and that is essential to understanding and documenting the credits.
If only it didn't cost so much! But there is a lot of value there and it costs money to produce, so I don't blame them.