You also get access the the ACM Digital Library, which has most of the papers from past Communications, Transactions, Proceedings etc in digital form (PDFs). Sadly they're often apparently scanned from paper so the files are large and the text isn't searchable, but it's still a tremendous resource.

A great many of the fundamental algorithms from the 1970s were published in one of the ACMs publications, and it can be a goldmine. There's a lot of good stuff there which still isn't well-known outside the academic world.

Ideally, of course, they'd make it available to everybody (not just ACM members). I hope they do.