Pingdom - Great Value and does just what you need

We bought Pingdom initially just to do quick and easy monitoring of our Customer facing web hosting to make sure all sites were up and responding, and would have been happy with just that functionality for the price paid. Afterwards we set up synthetic checks to log into these environments and validate basic functionality. Next, with some relatively minor code changes to our hosting, we started gathering Real User Experience data showing actual stats of page load times, user location and experiences. The only drawback we've found is that it's only capturing the initial page load - if you then do searches within that page you'll need some other way of capturing those stats.

That aside, we are very satisfied Customers and I'd be more than happy to recommend this