I'm looking for a good performance monitoring service for websites. I know about some of the available general monitoring services that check for uptime and notify you about unavailable services. But I'm specifically looking for a service with an emphasis on performance.
I.e., I would like to see reports with detailed performance statistics from multiple locations world-wide, with a break-down on how long it took to fetch the different website resources, including third-party scripts such as Google Analytics and so on (the report should contain similar details such as the FireBug Net tab). Are there any such services and if so, which one is the best?