The robot rules allow you to use any electronics component that costs less than $200 off the shelf. Therefore, I'm sure you can find all kinds of sensors that can legally be used. The common ones used include: The camera (:O), potentiometers, accelerometers, gyros, wheel encoders (optical and magnetic/gear tooth counters.) I've also heard of magnetic proximity sensors.
Almost all sensors (excluding the camera and any other TTL/Serial port device) are compatible with the EDU-RC. In general, if it runs on PWM, it'll work on either.
Both the FRC and EDU-RC use the same processor, and very similar code. With some minor adjustments for how you refer to the pins you're using, code for sensors can easily be transitioned between the two.
When you have a specific type of sensor in mind, you should search the white papers and forums, and ask any questions you have here. There is a lot of code for accelerometers, gyros, and encoders, as well as tutorial code for using interrupts, and for using the serial port to communicate, at Kevin Watson's site,
http://kevin.org/frc.
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