This blog post provides best iot projects using Things speak cloud

Forest fire prediction and alarm system using Thingspeak

Industrial Fault monitoring control and Prediction using Thingspeak  

Weather Prediction using Thingspeak

Smart home monitoring using thingspeak

Gas and Liquid level monitoring and alert system using Thingspeak

Pollution monitoring in  city using Thingspeak

Soil moisture and humidity level monitoring and Monsoon forecast based intelligent irrigation system 

Precision farming using Thingspeak