The Raspberry Pi has no built in analog to digital converters (ADC), which can limit the types of sensors it can interface to directly; digital only. A simple and inexpensive option for adding several channels of analog inputs is with Micochip’s MCP3008.
A subset of one on the projects I am working on with the Raspberry Pi is the ability to control miscellaneous RF items. A great start into this endeavor is radio frequency (434 MHz) remote control of a power outlet.
Adding a digital temperature sensor to the Raspberry PI is easy, especially with the DS18B20 1-Wire Digital Temperature Sensor Module. Each module has an unique address that allows them to be chained together on the same control line.