2/65/17 Update: A reader alerted me that these links don’t seem to work anymore. Sorry!
Thanks to Fifth Circuit Blog for this link to The Constitution of the United States of America, Analysis and Interpretation: Analysis of Cases Decided by the Supreme Court of the United States. It is provided by the Government Printing Office at its GPO Access website.
The site has a great index page. Took me all of five seconds to find online versions of the Code of Federal Regulations, Federal Register, and United States Code that are searchable, browsable, and have a find-by-citation function.
That’s barely scratching the surface. There’s plenty more, and all of it is free.