Forrest Mims III submitted an innovative use about studying heat islands in our Fall 2013 The Caliper newsletter. He has recently published an article for MAKE Magazine about tracking heat islands with LabQuest 2.
While temperature loggers work well, they require you to note times and locations during a transect so you can analyze the data. No notes are needed with a Vernier LabQuest 2, my favorite data logger for serious heat island studies.
After making a temperature transect across a city, you can send up to 1,000 temperature measurements to Vernier, which will return a Google map with a color-coded line that indicates the temperature along the route (violet being the coolest and red the warmest).