Useful Links
Linear Technology LTspice:  
A free op-amp simulation tool
Mancini, R., ed. Op Amps for Everyone: Design Reference. Texas Instruments, 2002. (PDF - 2.0MB)  
An excellent reference book for op-amp design.
OpAmps: Active Filter Synthesis Design Tool  
A simple tool from Analog Devices for designing active filters using voltage-feedback op-amps.
Sensors Web Portal  
References, hints, sources from the International Frequency Sensor Association (IFSA)
Robotics related products compiled by Kevin Dowling
Bill Buxton’s Directory of Sources for Input Technologies
Conferences
Sensors Expo  
Big trade show with tutorials and proceedings
IEEE Sensors  
Very large new state-of-the-art sensors conference
SPIE  
Old standby conference for sensors and applications
Transducers  
Emphasizes MEMs, but like IEEE Sensors
UIST  
ACM conference on user interface technology
SenSys, ISPN, etc.  
Sensor net conferences — not sensors…