Instruments and IFR
Pilot's Cafe IFR Quick Review Guide
When can I log an instrument Approach? (FAA Legal Clarification - InFO 15012)
AOPA - Safety Pilot vs Pilot Flying - Logging (PIC/SIC)
IFR Magazine - (and some free material)
IFR Magazine - ASR & No Gyro Approaches
Bold Method - ASR & No Gyro Approaches
See Books section for some additional reference materials.