We had discussed in class about how many books we thought there were in the world. This article explains how Google reached the estimated number of books.
This book, Digital History, exists in print form as well, but it is entirely available for free on the open web. It is written for historians who want to "go digital," so you as undergrads (and not necessarily History majors!) aren't exactly its audience, but the book is nevertheless excellent as an introduction to the underpinnings of the internet and the web.
You can download Wikipedia and only have it take up about 9 GB of space on your computer. It would definitely come in handy if you need to do research but don't have Internet access.
Although you should probably look a bit more into specific numbers, these facts are fascinating! For example, percentage of facebook users around the entire world and link to the very first website.