RFID Evolution:
Stage 1 - Passive (Identification), Require no External Power to Transmit
Stage 2 - Semi Passive (Sensing), Require no External Power to Transmit
Stage 3 - Active (Ad-hoc Communication) 
Stage 4 - Smart Sensor Network (Sensor Network)

Common and not so common uses for RFID:
Asset Real-Time Visibility, Automotive Monitoring (Tire Pressure), Automotive Electronic Systems, Bin Tagging, Equipment, Contamination, Controlled Substances Monitoring, Environmental Monitoring, Freshness Infratab-Freshtime Tag, Just-in-Time Ordering, Inventory Movement, Pallet Location, Telemedicine and Manufacturing Processes Control, Product Handling, Project Tracking, Prototype Tracking, Security Applications, Shipment Conditions, Supply Chain Management, Tamper and Damage Detection, Temperature Sensitive Explosives, Tool Theft

What you probably DID NOT know about RFIDs:
Apart from tracking, you can record an RFID's surrounding Environmental Conditions, including Acoustic (Seismometer), Temperature (Piezorrsistive Sensors), Capacitive Sensors, Pressure (Resonance Sensors-Strain Guage), Humidity, Inclination, Acceleration, Centrifugal Forces, Electromagnetic (Magnotometer), Optical Radiation (Light Detecting Diode), Vibration, Impact, Radiation, Pressure, Weight, Gas Sensors, Chemical Sensors (Carbon Monoxide), Thermocouple, and Light Exposure (any deviation from the normal or just plain recording). This provides you with the data necessary to make or take informed actions.

The omnipresent barcode labels that triggered a revolution in identification systems are being found to be inadequate in an increasing number of cases. The integration of sensors (especially the silicon based ones) into semi-passive RFID tags has recently generated a lot of interest among the RFID community. Only the silicon can meet the aggressive cost performance requirements of most new applications. Silicon based sensors are also benefiting from vast resources developed for the mainstream electronics: microprocessors, memories, and advanced linear microcircuits. The advantage of using Silicon Sensor Technology is not only in increased price-performance ratio, but also in an incredible volume manufacturing capability that IC manufacturing brings.

Generic Sensor Tag Logic Diagram