As I've mentioned before, there is something really cool about controlling external devices from code (especially humanoid robots). Now I've stumbled across a book that is dedicated to just that: Practical .NET 2.0 Networking Projects by Wei-Meng Lee.
This book walks the reader through several projects, detailing hardware setup and code for integrating with: a GPS receiver, a fingerprint reader, IR devices, RFID, webcam, and an ultrasonic sensor. While the book is a fun read and feels geared towards hobbyists, its projects have definite applications in the professional world as well.
One of the most interesting projects in the book details an RFID attendance application using the $39 Parallax RFID Reader and $2 Parallax Tag. Lee uses the $119 Javelin Demo Board to hook the reader to his PC but also mentions cheaper solutions. It's amazing how mainstream and inexpensive this technology is.
Whether you're a hobbyist looking for a fun time, or a professional working on your latest project, Practical .NET 2.0 Networking Projects has relevant and timely info for home and office.