Hello Kevin,
If your like me, than you have to totally own a concept before it sticks. Because of that, I always had to get multiple books on a given subject to fill in any holes. For a start on digital electronics, you might look for the book from Heath Kit's Digital logic course. It was intended for a technician level introduction, so the writing is thoughtful and not too deep. Beyond that, you'll need to get a textbook.
Student stores are the last place to look for good deals on books. If you have a friend that travels back and forth to India, he can get you the most awesome bargains on books as the same books are available there at about 20% our price. China is much cheaper
Another place to load up on books is from surplus shops and discount book stores located near engineering regions of the country. For example, I live near a semiconductor and electronics design hub, so companies and individuals are continually dumping books from their libraries.
Finally, one book that every electrical engineer should have (and is unfortunately expensive) is "The Art of Electronics." It makes a great Christmas gift from the over indulgent grandparents.
Best luck with your courses, don't stay out too late ; )
- Mike