To monitor Amazon Elastic Load Balancer (ELB) effectively, you can use CloudWatch, which provides key performance metrics that are available via AWS Management Console, command-line interface (CLI), and monitoring tools integrating the CloudWatch API. The AWS Management Console allows for setting up automated alerts and visualizing recent changes in individual metrics through graphs. Using the CLI enables quick spot checks and ad hoc investigations by querying for specific metrics. Monitoring tools integrated with CloudWatch offer extended functionality, such as correlating metrics from different infrastructure parts and accessing historical data. Additionally, ELB access logs can be used to investigate specific request issues, but may require dedicated log analytics tools for large traffic volumes.