Out of print books? Journals that your local library doesn't carry?
Google Book Search has been scanning and making available out of print books for perusal. Apparently they settled a lawsuit where they will be able to offer some copyrighted material also. My earliest introduction to Google Books came after attending the Alice Workshop at Santa Clara University in summer 2008. After I purchased an older edition of the book, then was given a pre-release copy of the latest edition, by the end of the summer the entire book was available on Google Books, meaning as an educator I would have no cost to teach my students computer science using Alice.
As a student myself, another resource that previously required an expensive license is the ERIC articles database, which offers almost every article ever written, which definitely helps post-secondary scholars conduct research.
These technologies phenomenally reduce the amount of time I physically have to spend in a library, the amount of money I have to spend on books or copies of pages of books, allows me to asynchronously pursue research and curiosity questions, and reduces the amount of paper wasted. They also represent quite a paradigm shift between my undergraduate and graduate educations! Isn't that what using technology in education is all about?