If you want to get a broad overview and understanding of sensor technologies you might as well learn from the best. Luckily, the MIT OpenCourseWare program is dedicated to making the same educational material, including course outlines, readings, lectures, assignments, and often videos, that are used to teach MIT students both at undergraduate and graduate levels.
For example, one of the program's current offerings is "MAS.836 Sensor Technologies for Interactive Environments:
"This course is a broad introduction to a host of sensor technologies, illustrated by applications drawn from human-computer interfaces and ubiquitous computing. After extensively reviewing electronics for sensor signal conditioning, the lectures cover the principles and operation of a variety of sensor architectures and modalities, including pressure, strain, displacement, proximity, thermal, electric and magnetic field, optical, acoustic, RF, inertial, and bioelectric. Simple sensor processing algorithms and wired and wireless network standards are also discussed. "
The MIT OpenCourseWare program material is covered by their Creative Commons License, and the best part is that it's absolutely free. All you have to do is bring your own intelligence, curiosity, and dedication. You can't beat that.