Great site overall; I just have a few observations/suggestions.
- For numeric specifications (gearbox reduction, motor speed, motor power, etc), narrowing down options by (user-specified?) ranges may be more useful than just selecting exact numbers.
- Sorting the tables by columns other than the default should be an option.
- Operating ranges and input voltage (especially if it's not 5V, though I think they all are 5V) may be useful for sensors.
- CIM compatible mounting is a useful specification to know for gearboxes.
- Weight would be useful for motors and gearboxes.
- Wheels and sprockets/pulleys would be my choices for categories to add next if you're looking to expand.