Microsoft Research has released an app that allows users of Windows Phone 8 devices to check their network speed. The app is easy to use and has a minimalist look to it. The user are also presented other information such as latency, jitter and packet loss.
Additional network information is available by sliding over including a user history of speed test runs. The app also has an additional use, this one for Microsoft;
"When you test a network connection using the App, certain characteristics of your device and the network connection will be sent to Microsoft to help improve our understanding of network quality and availability. If you consent, we may also collect information about your location at the time of the test. The data we collect is not associated with you, and will not be used to identify or contact you or for other purposes like targeted marketing."
You can pick up the app at the Windows Phone Store.