If you want to improve your drawing skills, get ideas for styles, and generally be inspired I would recommend you get hold of the following books. These are books that I found really valuable throughout my course, and were always a great source of reference.
This book, Architectural Drawing by David Dernie is a great book for students. It is jam packed full of styles, techniques and tips. Highly recommend.
Architectural Graphics by Francis DK Ching. I have recommended this book in previous posts, and for good reason. It covers all aspects of architectural drawing, particularly perspective drawings and architectural drawing systems.
Basics Architecture – Representation Techniques. I really enjoyed using this book throughout my course, mainly because it is full of examples of work, different styles and so on. A great reference point.
Architectural Drawing Course by Mo Zell is another comprehensive book for all those just starting out and in need of some tips and guidance.
Architects Pocket Book – Ok so this isn’t strictly a drawing book, but it has loads of information that is useful throughout. If you are only going to buy one book, buy this one. It is invaluable. It is the architecture students bible.